UniProt: Q9BKU4 (PHB1_CAEEL). WormBase: WBGene00004014 / Y37E3.9.
Gene name: phb-1 ("Mitochondrial prohibitin complex protein 1", prohibitin-1).
275 aa; single Band_7/SPFH (prohibitin/stomatin) domain (PF01145; IPR000163);
predicted coiled coil (residues 180–213). PANTHER family PTHR23222 (PROHIBITIN),
subfamily PTHR23222:SF0 (PROHIBITIN 1). ComplexPortal CPX-4114 (Prohibitin complex).
phb-1 is one of the two obligate subunits (with phb-2) of the mitochondrial
prohibitin (PHB) complex, a ring-shaped, high-molecular-weight assembly in the
mitochondrial inner membrane. The complex — not the isolated subunit — is the
functional unit; loss of either subunit abolishes the whole complex.
Obligate heterodimeric/ring complex with phb-2 in the mitochondrial inner
membrane. "Prohibitins in eukaryotes consist of two subunits (PHB1 and PHB2)
that together form a high molecular weight complex in the mitochondrial inner
membrane" and, in worm, "prohibitins in C. elegans form a high molecular weight
complex in the mitochondrial inner membrane similar to that of yeast and humans"
PMID:12794069.
The two subunits "bind to each other to form a heterodimer that is assembled into
a ring-like macromolecular structure at the inner mitochondrial membrane" and are
"interdependent for the formation of the complex, leading the absence of one of
them to the absence of the whole complex"
PMID:26092086
PMID:26092086.
Basis for GO:0035632 (mitochondrial prohibitin complex), GO:0005743 (mitochondrial
inner membrane). The IPI part_of annotation (PMID:19812672) is with phb-2
(WB:WBGene00004015).
Essential for embryonic viability and germline/gonad development. RNAi against
phb-1 or phb-2 "PHB proteins are essential during embryonic development and are
required for somatic and germline differentiation in the larval gonad"
PMID:12794069.
Restated later: prohibitin depletion "gives rise to a wide range of somatic and
germline defects, spanning from complete sterility to severely reduce brood sizes
and a morphologically abnormal somatic gonad"
PMID:26092086.
Basis for the WB IMP annotations to embryo development (GO:0009792), gonad
development (GO:0008406), oogenesis (GO:0048477), spermatogenesis (GO:0007283).
Altered mitochondrial biogenesis / organization on depletion. "a deficiency in
PHB proteins results in altered mitochondrial biogenesis in body wall muscle
cells" PMID:12794069.
Basis for GO:0007005 (mitochondrion organization). PHB-2 knockdown "influences ...
mitochondrial proliferation" PMID:19812672.
Context-dependent modulator of longevity, coupling to insulin/diapause signalling
and fat metabolism. "the mitochondrial prohibitin complex promotes longevity by
modulating mitochondrial function and fat metabolism in the nematode Caenorhabditis
elegans"; "prohibitin deficiency shortens the lifespan of otherwise wild-type
animals" but "knockdown of prohibitin promotes longevity in diapause mutants or
under conditions of dietary restriction"
PMID:19812672
PMID:19812672.
Later restated with genotype: "prohibitin deficiency shortens the lifespan of
otherwise wild type nematodes, while it dramatically extends the lifespan of the
already long-lived daf-2(e1370) insulin receptor mutants"
PMID:26092086.
Depletion "influences ATP levels, animal fat content and mitochondrial
proliferation in a genetic-background- and age-specific manner"
PMID:19812672.
Proposed complex-level molecular roles (from yeast/mammalian work, invoked for
the worm complex): membrane-bound chaperone that stabilizes newly synthesized
mitochondrial-encoded respiratory subunits, and/or membrane scaffold that recruits
membrane proteins to a specific lipid environment.
"The PHB complex has been shown to play a role in the stabilization of newly
synthesized subunits of mitochondrial respiratory enzymes in the yeast
Saccharomyces cerevisiae"
PMID:12794069.
"Several roles have been proposed for the mitochondrial prohibitin complex,
including a role as a membrane-bound chaperone, which holds and stabilizes newly
synthesised mitochondrial-encoded proteins ... and as scaffold proteins that
recruit membrane proteins to a specific lipid environment"
PMID:26092086
PMID:26092086.
Basis for GO:0050821 (protein stabilization, NAS). Note the qualifier: these are
proposed roles imported largely from yeast/human, not directly demonstrated
biochemically in worm.
The molecular mechanism of the prohibitin complex is genuinely unresolved.
The 2015 metabolome paper states plainly: "the true function of the mitochondrial
prohibitin complex remains elusive"
PMID:26092086.
Whether the complex works primarily as (a) a membrane-bound chaperone/holdase for
nascent inner-membrane proteins, (b) a scaffold that organizes a specific
cardiolipin/phospholipid microdomain and recruits client membrane proteins, or
(c) a regulator of the m-AAA protease (SPG-7/paraplegin) is not settled — the
literature proposes all three but demonstrates none as the mechanism in worm.
This is both a genuine biology gap and an ontology gap: "be the structural PHB
ring / organize an IMM lipid-protein microdomain" has no adequate GO molecular
function term, so a structural subunit reads as MF-dark.
How the SAME depletion produces OPPOSITE ageing outcomes (life-shortening in WT
vs life-extending in daf-2 / DR / mitochondrial mutants) is mechanistically
unexplained — the metabolic node the complex sits on is not defined.
The falcon report (Edison Scientific; genuine, 20-min run) reinforces and enriches
the picture above. Additional mechanistic context (grounded in review/primary
literature cited there; not all in our cached PMIDs, so used as context only, not as
verbatim supporting_text in the YAML):
None of these change the GOA annotation actions; they corroborate keeping the
complex/localization/mito-organization/protein-stabilization terms as core and the
developmental/behavioural terms as pleiotropic non-core, and they sharpen the two
recorded knowledge gaps (mechanism; opposite-longevity node).