Peroxisome Membrane Proteins Flashcards
What is the PEX19 binding sequence that most proteins targeted to the peroxisome membrane contain
11mer helical peptides with invariant basic residues flanked by hydrophobic amino acids e.g. KVLRLLQYLARFLAV
are peroxisome membrane targeting sequences cleaved
no as they are integral to the protein
where is the signal sequence found for single span peroxisome membrane proteins
for N term anchored proteins the sequence is found in the Nterm+the first transmembrane domain and in C term anchored proteins it is found in the C term + 1st TM domain
where is the signal sequence found for multi span peroxisome membrane proteins
At least 1 or 2 TM domains plus flanking regions comprise the signal sequence
What is the evidence to suggest that there are different genetic requirements to import membrane proteins from matrix proteins
matrix import mutants are still able to effectively integrate membrane proteins
which 3 proteins comprise the peroxisome membrane protein receptors
PEX3, 19 and 16
what is the role of PEX3
it is a membrane receptor for PEX19
what is the role of PEX19
It is the proposed chaperone for PMPs which is predominantly cytosolic. It bids newly synthesised peroxisomal proteins via its globular C terminal domain and binds PEX3 via its flexible Nterm
how is binding of PMPs to PEX19 enhanced
by farnesylation of PEX19. this is also thought to enhance insertion
what is the role of PEX16
potentially PEX3 receptor, plays a role in insertion or cats as a PMP receptor- the role is not clear but it is implicated in PMP import in mammals
what family of proteins regulate peroxisome division
PEX11 family
what is the role of PEX11 in peroxisome devision and how then is division facilitated
it binds the surface of peroxisomes and causes it to tubulate. Division factors which are dynamin GTPases are recruited which are involved in division
How are peroxisomes inherited from mother to daughter cells in yeast
they move along the actin based skeleton in yeast and microtubules in mammals. In yeast they are anchored to actin by binding Imp1p. Imp2 acts as a receptor to recruit an isoform of myosin which can move the peroxisome along the actin into the daughter cell.
what are the 3 models to describe where peroxisomes come from
derivation of the ER
autonomous organelles
hybrid model
what does the model which suggests peroxisomes are derived from the ER outline
it suggests that peroxisomes are offshoots from the ER system. mRNA translated into peroxisome proteins were transported into the ER then into a vesicle and then budded off to form peroxisomes
what was the evidence that peroxisomes derived from the ER
apparent physiscal connections/close proximity to the ER and cell fractionation studies in which ER and peroxisomal proteins were found in the same fraction
what does the model which suggests peroxisomes are autonomous organelles outline
that we have always had peroxisomes and that peroxisomal proteins were targeted to small organelles which grew and could be divided and passed onto daughter cells
what does the hybrid model for peroxisomal origin outline
it suggests that the ER does play a role however mutants that lack detectable peroxisomes can regain them when the missing gene product is supplied. PEX3 when first synthesised will first go to the ER and then to peroxisomes at which point peroxisomal import can occur.
describe how scPEX15p is inserted into the ER and then transported to peroxisomes for insertion into the peroxisomal membrane
the complex called guided entry of tail anchored proteins (GET) facilitates insertion into the ER. vesicles containing scPex15p and scpex3p can be formed from ER in vitro which transport it to peroxisomes
give an example of a PEX7 mutant disorder
RCDP (group B) causing growth defects, cataracts, epiphyseal calcifications etc. also results in low plasmalogens and high levels of phyantic acid
give an example of a PEX7 mutant disorder
group A disorders e.g. Zellweger syndrome. results in loss of all matrix proteins causing severe neurological and hepatic dysfunction and ultimately early death. present with low levels of plasmalogens (ether linked lipids made in peroxisomes) and high levels of substrates which should be oxidised via beta oxidation of fatty acids such as VLCFA
give an example of a disorder caused by mutation of an individual peroxisomal enzyme
X-linked adrenoleukodystrophy
what is the result of PEX14 mutations in plants
defects in photorespiration, matrix protein import and b oxidation
what is the result of PEX5 mutations in plants
defects in b oxidation
