REVIEW ARTICLE
Dynamin-related proteins and Pex11 proteins in
peroxisome division and proliferation
Sven Thoms and Ralf Erdmann
Ruhr-University-Bochum, Medical Faculty, Institute of Physiological Chemistry, Bochum, Germany
Introduction
Peroxisomes (or microbodies) are single-membrane
bound organelles comprising plant glyoxisomes, kineto-
plastid glycosomes, Woronin bodies and peroxisomes
in the narrow sense. Peroxisomes are very diverse in
their metabolic functions. Depending on species, cell
type, and environmental conditions, peroxisomes may
perform different metabolic activities, including fatty
acid a- and b-oxidation, alcohol oxidation, ether-lipid
biosynthesis, glycolysis, and glycerol metabolism [1]. In
contrast to their metabolic heterogeneity, the biogenesis
of peroxisomes seems to follow a common pathway,
relying on conserved proteins, the so-called peroxins.
Most peroxins are involved in matrix protein import
or in formation of the peroxisomal membrane [2]. A
surprisingly large number of peroxins, however, is
required for the proliferation and inheritance of these
organelles.
The relevance of peroxisomes for human health is
underscored by the existence of peroxisomal biogene-
sis disorders (PBDs) [3,4]. These diseases are charac-
terized by defects in peroxisome protein import,
which leads to an impairment of all peroxisomal
functions, with the accumulation of a- and b-oxida-
tion substrates (such as very long chain fatty acids
or phytanic acid) and a reduction in plasmalogen
levels. PBDs are associated with a number of more
pleiotropic abnormalities, such as hypotonia, develop-
mental delay, defects in neuronal migration and
apoptosis, and hepatic and renal problems. At the
cellular level, mitochondria can also be affected
in PBDs, probably because of their metabolic inter-
relation with peroxisomes [5–7].
Keywords
dynamin-related protein; dynamin;
endoplasmic reticulum; GTPase; organelle
division; peroxisome proliferator-activated
receptor; peroxisome; PEX11; VPS1; yeast
Correspondence
R. Erdmann, Systems Biochemistry,
Institute of Physiological Chemistry,
Ruhr-University-Bochum, 44780 Bochum,
Germany
Fax: +49 234321 4266
Tel: +49 234322 4943
E-mail: ralf.erdmann@rub.de
(Received 28 July 2005, accepted 26 August
2005)
doi:10.1111/j.1742-4658.2005.04939.x
The abundance and size of cellular organelles vary depending on the cell
type and metabolic needs. Peroxisomes constitute a class of cellular organ-
elles renowned for their ability to adapt to cellular and environmental
conditions. Together with transcriptional regulators, two groups of per-
oxisomal proteins have a pronounced influence on peroxisome size and
abundance. Pex11-type peroxisome proliferators are involved in the proli-
feration of peroxisomes, defined here as an increase in size and ⁄or number
of peroxisomes. Dynamin-related proteins have recently been suggested to
be required for the scission of peroxisomal membranes. This review surveys
the function of Pex11-type peroxisome proliferators and dynamin-related
proteins in peroxisomal proliferation and division.
Abbreviations
DRP, dynamin-related protein; GED, GTPase effector domain; PBD, peroxisomal biogenesis disorder; PCD, programmed cell death;
PPAR, peroxisome proliferator-activated receptor alpha; PPP, Pex11-type peroxisome proliferators; PPRE, peroxisome proliferator-responsive
elements; PRD, proline- and arginine-rich domain.
FEBS Journal 272 (2005) 5169–5181 ª2005 FEBS 5169
The abundance of peroxisomes in a cell is regula-
ted by a number of as yet incompletely understood
processes. These can – at least conceptually – be divi-
ded into (a) peroxisome proliferation by division, (b)
peroxisome de novo biogenesis, (c) peroxisome inherit-
ance, and (d) peroxisome degradation by pexophagy,
an autophagy-related process. Our knowledge about
the relative contributions of these processes to main-
tain or establish a certain number of peroxisomes in
a cell, is rather limited. However, at least two classes
of proteins are involved in controlling peroxisome
number and division. This review offers an overview
of these two classes, namely dynamin-related proteins
(DRPs) [8], and Pex11-type peroxisome proliferators
(PPPs). Proliferation is understood here as a process
that leads to an increase in size and ⁄or number of
peroxisomes.
Peroxisome proliferation at large
The idea of peroxisome biogenesis by ‘growth and
division’ was put forward in a very influential review
20 years ago [9]. Based on the post-translational
import of matrix proteins and one major membrane
protein [10,11], it has become a largely accepted
dogma that membrane proteins, as well as matrix pro-
teins, are imported post-translationally from the cyto-
sol. In the light of recent research, however, a
substantial contribution from the endoplasmic reticu-
lum seems likely [12–16].
In yeast, fatty acids cause the proliferation of per-
oxisomes [17] and the transcriptional up-regulation of
peroxisomal b-oxidation enzymes. This response is
mediated by the oleate response element, together with
the transcription factor complex, Pip2–Oaf1 [18–20],
and the transcription factor, Adr1 [21,22]. Adr1 regu-
lates expression of the peroxisome-specific acyl-CoA
oxidase FOX1 ⁄POX1 as well as of PEX11 [23].
Early work on peroxisome division in Candida
boidinii has shown that small peroxisomes carrying an
incomplete set of matrix proteins divide and mature by
protein import only after a large number of immature
peroxisomes have been formed [24]. This work was
extended by a comparative study using different
growth conditions to induce peroxisomes [25]. It was
found that certain peroxisome-inducing conditions,
such as d-alanine, methanol or oleate, up-regulate per-
oxisome-resident enzymes in a specific manner, rather
than causing a general increase in peroxisome number.
These findings underscore the variability and versatility
of these organelles.
Five different immature peroxisome populations
have been identified in the yeast Yarrowia lipolytica,
which are described to mature by movement through
an ordered pathway [26]. In the course of peroxisome
maturation, acyl-CoA oxidase moves in a heteropenta-
meric complex from the matrix to the inner membrane
of the peroxisome. The membrane-bound pool of acyl-
CoA oxidase interacts with Pex16, which is also mem-
brane bound inside the peroxisome. The substrate–
Pex16 interaction inhibits the negative influence of
Pex16 on peroxisome division and thereby allows per-
oxisome division [27].
‘Growth and division’ do not follow the same course
in all species. In Y. lipolytica, and similarly in Hansen-
ula polymorpha, peroxisomal vesicles do not divide
before they have matured after the import of matrix
proteins [28,29]. In contrast, in C. boidinii, immature
peroxisomes that have only acquired part of their
matrix protein content seem prone to divide [30]. In
human cells, however, both mature and immature per-
oxisomes have the capability to divide [31]. Whether
these differences truly reflect species differences, or if
they are a result of different methods, remains to be
evaluated.
In mammalian cells, peroxisome proliferator-activa-
ted receptor alpha (PPARa) is critical for peroxisome
induction [32]. PPARabelongs to the superfamily of
ligand-activated nuclear transcription factors [33–36].
The ligands of these receptors are lipids, lipophilic
substances, together with synthetic hypolipidaemic
drugs, or peroxisome proliferators. PPARs bind to
peroxisome proliferator-responsive elements (PPREs)
in a heterodimer with retinoid X receptor. PPARais
expressed in adipose tissue and liver. Its target gene
products are involved in lipid catabolism such as
fatty acid uptake, storage and oxidation (in peroxi-
somes and mitochondria), and in lipoprotein assem-
bly and transport. Two other PPAR subtypes have
been described: PPARb(¼PPARd) and PPARc.
PPARbis ubiquitously expressed, and PPARcis
expressed mainly in adipose tissue, but also in colon,
the immune system, and in the retina. PPARccon-
trols the differentiation of adipose tissue and fatty
acid storage and mobilization. In spite of their name,
PPARband PPARchave not been associated with
peroxisome proliferation. PPARs are involved in dis-
eases such as diabetes, obesity, atherosclerosis, and
cancer, which explains the high interest in pharmaco-
logical control of these proteins. A clear-cut evalua-
tion of PPAR effects, however, is hampered by
species differences between rodents and humans,
which might, in part, be explained by different
expression levels [37] resulting from differences in the
PPREs [38], leading to nonconserved responses to
peroxisome proliferators.
Peroxisome proliferation S. Thoms and R. Erdmann
5170 FEBS Journal 272 (2005) 5169–5181 ª2005 FEBS
Pex11 proteins in peroxisome
proliferation
Pex11 was the first protein identified as being
involved in peroxisome proliferation or division in
yeast [39,40]. Loss of PEX11 leads to reduced per-
oxisome abundance with giant peroxisomes [39].
Similarly, depletion of Trypanosoma brucei PEX11
(TbPex11) reduces glycosome number and size [41].
Conversely, overexpression of PEX11 promotes per-
oxisome elongation and proliferation in yeast [40],
and TbPex11 overexpression causes elongation and
clustering of glycosomes [41].
Pex11-mediated peroxisome division is described as
a process consisting of up to four partially overlapping
steps [42], namely (a) the insertion of Pex11 into the
membrane, (b) the elongation of peroxisomes, (c) the
segregation of Pex11 and the formation of Pex11-
enriched patches, and (d) the division of peroxisomes
(Fig. 1).
In all organisms studied to date, microbody abun-
dance can be increased by the expression of extra
copies of PEX11. Recently, this was confirmed for
Penicillium chrysogenum, where PEX11 overexpression
likewise leads to the proliferation of microbodies and
an increase in penicillin production, which is not
accompanied by a significant increase in penicillin
biosynthesis enzymes [43]. PEX11-induced penicillin
overproduction in P. chrysogenum could be explained
by increased metabolite transport through the micro-
body membrane and might prove commercially rele-
vant.
Pex11 function has mostly been analysed in Sac-
charomyces cerevisiae, trypanosoma, and mammals.
Diverse as the peroxisome functions are in these
organisms, a requirement of the three Pex11 isoforms
seems to be a common factor.
Three Pex11 isoforms in mammals
In mammals, three isoforms of Pex11 – Pex11a,
Pex11b, and Pex11c– have been identified [42,44,45].
All three isoforms are described as membrane proteins
with two transmembrane domains and both termini
exposed to the cytosol.
PEX11ais inducible by inducers of peroxisome pro-
liferation. Its expression is highest in liver, kidney,
heart, and testis [42,45–47]. A PEX11aknockout
mouse is morphologically indistinguishable from a
wild-type mouse, with no obvious effect on peroxisome
number or metabolism [47], suggesting that its loss can
be largely compensated by other Pex11 isoforms. The
induction of peroxisome proliferation through PPARa
by ciprofibrate does not require PEX11a, but leads to
the clustering of mitochondria around lipid droplets
and abnormally straight mitochondrial cristae [47]. In
contrast, the nonclassical peroxisome proliferator,
phenylbutyrate, works independently of PPARa, but
is PEX11-dependent [47]. Phenylbutyrate also induces
the adrenoleucodystophy-related gene (ALDP) [48].
The second isoform of Pex11, Pex11b, is not indu-
cible by peroxisome proliferators. It is constitutively
expressed in most tissues [44]. Overexpression of
PEX11binduces peroxisome proliferation to a
greater extent than overexpression of PEX11a[42].
The knockout of PEX11bin mice leads to neonatal
lethality with a number of defects reminiscent of
Zellweger, including developmental delay, hypotonia,
neuronal migration defects, and neuronal apoptosis
[49]. These mice are, however, only mildly affected
in peroxisome protein import and metabolism
(reduced ether lipid biosynthesis) [49]. This prompts
the idea that some of the pathological features of
Zellweger are not caused by gross metabolic distur-
bances but rather by subtle effects on signalling
pathways involving peroxisomal substrates or prod-
ucts. In cases where only a limited number of
metabolites would have to be normalized, this could
raise hope for therapeutic intervention in peroxi-
somal diseases.
Knockout mice with deletion of both PEX11aand
PEX11bstill contain peroxisomes and are only mildly
affected in peroxisomal metabolic activity [49]. These
mice also die early after birth with severe neurological
defects [49]. In summary, PEX11aseems to be respon-
sible for peroxisome proliferation in response to exter-
nal stimuli, whereas PEX11bis required for
constitutive peroxisome biogenesis.
The third isoform, Pex11c, is constitutively
expressed in liver [50] and might have a redundant
function with Pex11b, although it is with 22% amino
Fig. 1. Model of peroxisome proliferation and division. (1) Elonga-
tion. (2) Segregation. (3) Constriction. (4) Fission ⁄division. For
details see the text.
S. Thoms and R. Erdmann Peroxisome proliferation
FEBS Journal 272 (2005) 5169–5181 ª2005 FEBS 5171
acid identity less similar to Pex11bthan Pex11ais to
Pex11b(40% amino acid identity).
New members of the PEX11 family in yeast
Recently, proteins with a weak similarity to Pex11
have been identified in S. cerevisiae [51–53]. The new
Pex11 proteins, Pex25 and Pex27, are more similar to
each other (18% identity) than to Pex11 (9% iden-
tity). Pex25 (45 kDa) and Pex27 (44 kDa) have a
higher molecular mass than Pex11 (27 kDa); in fact,
they appear to have an N-terminal extension when
compared with Pex11. All three proteins localize to
peroxisomes. Pex25 behaves as a peripheral membrane
protein [51].
The knockout of PEX25 has a stronger growth
defect on oleic acid than the deletion of PEX27. The
double knockout of PEX25 and PEX27 has about the
same growth defect on oleic acid as the PEX25 single
knockout [51,52]. Growth of this double deletion can
be restored by low copy expression of PEX25 or high
copy expression of PEX27 [51]. The triple deletion of
all three PPPs is unable to grow on oleic acid [51],
indicating that at least one of the Pex11 proteins is
required for peroxisome biogenesis. The growth defect
of the triple mutant can be alleviated by the over-
expression of PEX25, but not by the overexpression of
PEX27 or PEX11 [51]. The triple deletion shows a
matrix protein import defect, even under conditions
where peroxisome proliferation is not induced by oleic
acid [51]. In the triple mutant, thiolase is expressed at
normal levels, indicating that Pex11 family members
are not involved in fatty acid signalling.
Single and double deletions of members of the PPPs
contain enlarged peroxisomes [51–53], underscoring the
idea that Pex11 proteins are involved in peroxisome
proliferation. Conversely, the overexpression of each
of the family members causes peroxisome proliferation
or enlargement [51,52]. The overexpression of PEX25
also causes kamellae around the nucleus [51]. PEX25 is
induced by oleic acid [53,54] through an unusual oleate
response element in its promotor [54], whereas PEX27
is not induced at all on oleic acid [51,52]. Thus, in
oleic acid-induced cells, the Pex11 expression level is
highest and the Pex27 expression level lowest. All
Pex11 proteins interact with themselves [51,52,55].
They are likely to form homo-oligomers or homo-
dimers. Additionally, Pex25 and Pex27 interact with
each other [51,52].
In trypanosoma, there are also two additional Pex11
isoforms, GIM5A and GIM5B. These two proteins are
nearly identical in sequence and show weak similarity
to Pex11. Both are 26 kDa, have two putative
transmembrane domains, and assemble into hetero-di-
mers [56]. A GIM5 reduction leads to a lower phos-
phatidylcholine ⁄phosphatidylethanolamine ratio and a
decrease in ether lipids [57], which could increase
membrane fluidity. Trypanosomes with reduced GIM5
levels have enlarged glycosomes, which are more fra-
gile than wild-type glycosomes [57].
Thus, it turns out that mammals, S. cerevisiae and
trypanosomes have three Pex11 homologues each.
Whether they represent an early or a late diversifica-
tion of an ancestral Pex11 function could not be deter-
mined because of their low sequence similarity.
Pex11 and perilipin
In mouse, PEX11aand the lipid body protein perilipin
are regulated from a single PPRE that is situated
between the two genes [58]. As a consequence of this
gene arrangement, PEX11a, which is expressed mainly
in the liver, and perilipin, whose expression is limited
to adipose tissue, can be competitively regulated by
PPARaand PPARc, respectively. This is not only a
noticeable example of gene clustering in mammals [59],
it also indicates that peroxisome proliferation can be
induced by switching from PPARcto PPARa. Fur-
thermore, the common regulation of Pex11 and peri-
lipin indicates metabolic association of peroxisomes
with lipid storage function [60].
New proteins affecting peroxisome number
Pex28 and Pex29 are two recently identified proteins
with a weak similarity to Pex24 from Y. lipolytica.
Pex24 is an oleic acid-inducible peroxisomal integral
membrane protein that is required for growth on oleic
acid [61]. Mutants of PEX24 have no apparent peroxi-
somes, they mislocalize peroxisomal matrix and mem-
brane proteins, yet contain vesicular structures with
some peroxisomal proteins [61]. Pex28 and Pex29 from
S. cerevisiae are also peroxisomal membrane proteins
[62]. They are, however, not inducible by oleic acid.
Double or single deletions of the two proteins show an
increased number of small and clustered peroxisomes.
Pex23 from Y. lipolytica is an oleic acid-inducible
membrane protein [63]. Three proteins from bakers
yeast, which have been termed Pex30, Pex31, and
Pex32, show sequence similarity to Pex23 and have
also been localized to the peroxisomal membrane [64].
Pex30 and Pex32 are induced by oleic acid. These new
peroxins are partially redundant and partially interact
with each other. Deletions of these latest additions to
the PEX list show an increase in peroxisome numbers,
enlarged or clustered peroxisomes, so that they have
Peroxisome proliferation S. Thoms and R. Erdmann
5172 FEBS Journal 272 (2005) 5169–5181 ª2005 FEBS
been described as regulators of peroxisome size and
number [64]. Based on an epistasis analysis, Pex30–32
are placed downstream of Pex28 and Pex29 [64].
Models for Pex11 function
The eight peroxins – Pex11, Pex25, Pex27, Pex28,
Pex29, Pex30, Pex31, and Pex32 – have a more or less
pronounced effect on peroxisome size and number. To
date it is unclear how this effect is exerted. Different
explanations are possible, as follows:
(a) Some of these proteins might be directly involved
in fatty acid metabolism [65]. Yeast mutants lacking
PEX11 exhibit a defect in the b-oxidation of medium-
chain fatty acids [65]. On this basis, it was suggested
that Pex11 plays a primary role in medium-chain fatty
acid metabolism and promotes peroxisome division
only indirectly [65]. In addition, there is evidence that
Pex11 can promote peroxisome proliferation in the
absence of metabolism [66].
(b) The peroxins might be metabolite transporters or
porins [57]. This would, however, require a rather
broad substrate specificity of these proteins, with fatty
acid and glycolytic substrates being transported in clas-
sical peroxisomes and glycosomes, respectively.
(c) They might be structural components of the per-
oxisomal membrane. For PPPs such an explanation is
likely, yet nonexclusive with other explanations. They
are by far the most abundant proteins of the peroxi-
somal membrane (shown in yeast and trypanosomes).
Thus, they might directly and specifically shape the
peroxisomal membrane. Overexpression of other per-
oxisomal membrane proteins has been reported not to
induce peroxisome proliferation [66].
(d) They might recruit other proteins to the mem-
brane. The recognition of Pex25 as a receptor for the
GTPase Rho1 [67] could be a first step of research into
this direction.
In summary, there are some models on how PPPs
(together with Pex30 to Pex32) might affect peroxi-
some number. These models are nonexclusive with
each other, and the mechanism of action will not be
the same for all PPPs. In the light of the different roles
that have been suggested for Pex11, it is possible that
PPPs are multifunctional enzymes. Recently, another
class of proteins has come into focus. These are sug-
gested to affect peroxisome division in a more direct
way.
DRPs in peroxisome division
Before addressing the role of DRPs in peroxisome
division, we will briefly introduce (a) conventional
dynamins, (b) the structural and physicochemical prop-
erties of DRPs and (c) DRPs engaged in the division
of endosymbiotic organelles.
Dynamins are involved in endocytosis and
intracellular trafficking
Dynamins are GTPases involved in intracellular fis-
sion processes [68–70]. Five domains have been identi-
fied in conventional dynamins: a highly conserved
N-terminal GTPase domain, a less conserved ‘middle
domain’, and a pleckstrin homology domain that
mediates interactions with phosphatidylinositol-phos-
phates (Fig. 2). The C terminus comprises the
GTPase effector domain (GED), which activates
GTPase activity and mediates self-assembly, and a
proline and arginine-rich domain (PRD) that mediates
interactions with SH3 domains of effector proteins of
the actin cytoskeleton.
Dynamins are required in phagocytosis and in caveo-
lae- and clathrin-dependent endocytosis [71]. Of the
three conventional mammalian dynamins, Dynamin1 is
neuron-specific, Dynamin2 is expressed in all tissues
and Dynamin3 is found in brain, lung, heart, testis and
blood cells.
The role of dynamin in clathrin-mediated endocytosis
emerged from the study of the temperature-sensitive
mutant shibire in Drosophila melanogaster [72]. Shibire
shows a paralytic phenotype that is probably caused by
a defect in the reuptake of synaptic vesicles at the presy-
naptic membrane and subsequent synaptic vesicle deple-
tion at the neuromuscular junction [73]. Electron
micrographs of shibire nerve termini show the formation
of clathrin-coated buds unable to sever from the mem-
brane. Dynamin localizes to the necks of these buds [73–
75]. Recently, a mutation in the PH domain of DNM2
has been identified as the cause of one form of Charcot-
Marie-Tooth disease, a neuromuscular degenerative dis-
order [76], thereby providing the first link between a
classical dynamin and an inheritable human disease.
Dynamin biochemistry and structure
In vitro, dynamin assembles into rings upon dilution
into buffers of low ionic strength [77]. Furthermore,
Fig. 2. Domain structure of dynamins and dynamin-related proteins
(DRPs). GED, GTPase effector domain; MD, middle domain; PH,
pleckstrin homology; PRD, proline- and arginine-rich domain.
S. Thoms and R. Erdmann Peroxisome proliferation
FEBS Journal 272 (2005) 5169–5181 ª2005 FEBS 5173