HSPA4, also called Apg2, is an Hsp110-family chaperone that serves as a nucleotide-exchange factor for Hsc70. Together with Hsp70 and J-domain co-chaperones it supports refolding and disaggregation of proteins. Its substrate-binding and distinctive C-terminal regions tune Hsc70 engagement and nucleotide exchange.
Apg2/HSPA4 belongs to the Hsp110 branch of the Hsp70 superfamily. Human biochemical work measures its effect on the Hsc70 ATPase cycle, aggregate binding and refolding. The concentration dependence is important: low Apg2 stimulates the system, while high concentrations can inhibit it. Its acidic and C-terminal regions regulate association and exchange. Those studies do not make HSPA4 the Hsp70L1 subunit of the Mpp11/Hsp70L1 ribosome-associated complex. General chaperone activity is transferable at a broader level than membership of a specific ribosome-bound assembly. A Tom40-import annotation must be checked in the complete original paper, since its abstract emphasizes Hsp90 rather than resolving every chaperone tested.
From PMID:30521813(https://pubmed.ncbi.nlm.nih.gov/30521813/):
Hsp110s support the refolding of aggregated polypeptides acting as specialized nucleotide exchange factors of Hsp70. We have studied how Apg2, one of the three human Hsp110s, regulates the activity of Hsc70 (HspA8), the constitutive Hsp70 in our cells.
The exact target is A0A9L0S5Z5, not an arbitrary horse record with a matching name. The reproducible paired-sequence analysis records identity, coverage and internal gaps. It supports homology but is not a reciprocal orthology test. Molecular properties are transferred only with the relevant domain, targeting and paralog constraints. The prediction-time sequence is not independently verified.
The following annotation scopes need source-specific follow-up: ATP hydrolysis activity, chaperone-mediated protein complex assembly, nucleus, protein binding, protein import into mitochondrial matrix, response to unfolded protein. Experimental annotations are not removed merely because a cached abstract omits the gene or a specific assay. High-throughput protein-binding rows require their actual partner or complex context before replacement with an informative molecular function.
Research provenance: external Falcon/Edison was attempted with Perplexity fallback. Some requests returned HTTP 429 and fallback returned insufficient-quota HTTP 401; successful external reports are preserved separately. Primary-source manual synthesis is explicitly labeled manual where no external report was available.