Bap (Sil1) regulates the molecular chaperone BiP by coupling release of nucleotide and substrate

Abstract

BiP is the endoplasmic member of the Hsp70 family. BiP is regulated by several co-chaperones including the nucleotide-exchange factor (NEF) Bap (Sil1 in yeast). Bap is a two-domain protein. The interaction of the Bap C-terminal domain with the BiP ATPase domain is sufficient for its weak NEF activity. However, stimulation of the BiP ATPase activity requires full-length Bap, suggesting a complex interplay of these two factors. Here, single-molecule FRET experiments with mammalian proteins reveal that Bap affects the conformation of both BiP domains, including the lid subdomain, which is important for substrate binding. The largely unstructured Bap N-terminal domain promotes the substrate release from BiP. Thus, Bap is a conformational regulator affecting both nucleotide and substrate interactions. The preferential interaction with BiP in its ADP state places Bap at a late stage of the chaperone cycle, in which it coordinates release of substrate and ADP, thereby resetting BiP for ATP and substrate binding.

Recent advances in the structural and mechanistic aspects of Hsp70 molecular chaperones

“…Thus, BiP binding occurs to an unfolded C H 1 domain, and the recognition is mediated by linear sequences, well mimicked by peptides but not entirely as the lid does not close over the peptide-binding pocket (43). The timing and coordination of the assembly of the full IgG is complex and influenced by co-chaperones as well as other factors (59). Again, this system exemplifies the exploitation of Hsp70's chaperone functions for a physiological need.…”

Biallelic mutations in EXOC3L2 cause a novel syndrome that affects the brain, kidney and blood

“…The previously reported DWM-associated genes play a role in migration of mossy fibres in the brain ( ZIC1 and ZIC4 ),42 cell fate determination, proliferation and differentiation ( FOXC1 ),43 unfolded protein response and endoplasmic reticulum-chaperon function ( SIL1 )44 or cellular interactions with extracellular matrix ( NID1 and LAMC1 ) 16…”

Function, evolution, and structure of J-domain proteins

“…But, some NEFs are more than nucleotide exchange factors. Claes Andréasson highlighted how armadillo-type NEFs in both the cytosol and endoplasmic reticulum employ a substrate-mimicking release domain to prevent rebinding of substrates to Hsp70, subsequent to exchange-accelerated substrate release (Gowda et al 2018;Rosam et al 2018). Interestingly, BAG domain NEFs carry similar unstructured domains required for efficient substrate release (Rauch et al 2016).…”