Disease relevance of SEC63

• The gene corresponding to one complementation group (NPL1) encodes a protein with homology to DnaJ, an Escherichia coli heat shock protein. npl1-1 is allelic to sec63, a gene that affects transit of nascent secretory proteins across the endoplasmic reticulum [1].

High impact information on SEC63

• Multiple BiP molecules associate with each translocation substrate following interaction with the J domain of the Sec63p component of the Sec complex [2].
• Here we show that Sec61, Sec62 and Sec63 are assembled with two additional proteins into a multisubunit membrane-associated complex [3].
• Recently, the homolog of yeast protein Sec63p was identified in dog pancreas microsomes [4].
• Sec63p and Kar2p are required for the translocation of SRP-dependent precursors into the yeast endoplasmic reticulum in vivo [5].
• There is both genetic and biochemical evidence that Kar2p interacts with Sec63p, an ER membrane protein containing both luminal and cytosolic domains that is involved in protein translocation across the membrane [6].

Biological context of SEC63

• The SEC61, SEC62 and SEC63 yeast gene products are membrane components of the apparatus that catalyses protein translocation into the endoplasmic reticulum (ER) [7].
• To identify proteins that might interact and/or function with SEC63p, we cloned a high copy suppressor (HSS1) of the temperature-sensitive lethal phenotype of the sec63-101 mutant [8].
• To clarify the roles of Kar2p (BiP) and Sec63p in translocation across the ER membrane in Saccharomyces cerevisiae, we have utilized mutant alleles of the essential genes that encode these proteins: kar2-203 and sec63-1 [9].
• These findings show that phosphorylation of Sec63p is required for tightly recruiting the putative signal-sequence-binding subunit Sec62p to the Sec complex [10].

Anatomical context of SEC63

• The translocation defects of two mutants (sec62 and sec63) have been reproduced in vitro. sec63 microsomes display low and thermolabile translocation activity for prepro-alpha-factor (pp alpha F) synthesized with a cytosol fraction from wild type yeast [11].
• To investigate the role of these proteins in cotranslational translocation, we examined the import of invertase into wild-type, sec63, and kar2 mutant yeast membranes [12].
• Alternatively, by affecting ER and nuclear envelope assembly, npl1 may indirectly alter assembly of proteins into the nucleus [1].
• Sordarin Derivatives Induce a Novel Conformation of the Yeast Ribosome Translocation Factor eEF2 [13].

Associations of SEC63 with chemical compounds

• Sec63p associates with several other proteins, including Sec61p, a 31.5-kDa glycoprotein, and a 23-kDa protein, and together with these proteins may constitute part of the polypeptide translocation apparatus [14].
• We show that Sls1p stimulates in a dose-dependent manner the binding of ScKar2p on the lumenal J domain of Sec63p fused to glutathione S-transferase [15].
• Exchanging either threonine 652 or threonine 654 against the nonphosphorylatable alanines in Sec63p impairs the binding to Sec62p and interferes with the efficient translocation of proteins across the membrane of the endoplasmic reticulum [10].

Physical interactions of SEC63

• Finally, we determine the authentic N-terminus of Sec62p and describe interacting subdomains of both Sec62p and Sec63p [16].
• In the presence of ATP, under conditions in which BiP can bind to Sec63p, the secretory precursor passes from the cytosol into the lumen through a membrane channel formed by Sec61p [17].

Enzymatic interactions of SEC63

• We show that Sec63p is phosphorylated at its C-terminal domain by the protein kinase CK2 and that this phosphorylation strengthens the interaction between the cytosolic domains of Sec63p and Sec62p [10].

Regulatory relationships of SEC63

• Finally, we found that the soluble Sec63p lumenal domain inhibited efficient precursor import into proteoliposomes reconstituted so as to incorporate both BiP and the fusion protein [18].
• Moreover, Sls1p is shown to promote the Sec63p-mediated activation of Kar2p's ATPase activity [15].

Other interactions of SEC63

• A Sec63p-BiP complex from yeast is required for protein translocation in a reconstituted proteoliposome [19].
• The new mutants, sec62 and sec63, are thermosensitive for growth and accumulate a variety of soluble secretory and vacuolar precursors whose electrophoretic mobilities coincide with those of the corresponding in vitro translated polypeptides [11].
• The Sec63p complex restores translocation activity to reconstituted vesicles that are prepared from a sec63-1 strain, or from cells in which the SEC66 or SEC67 genes are disrupted [19].
• The region common to all DnaJ homologues (termed the J domain) from Scj1p can be swapped for a similar region in Sec63p, which is known to interact with Kar2p in the ER lumen, to form a functional transmembrane protein component of the secretory machinery [20].
• However, only three amino acid changes in the Sis1p J domain render the Sec63 fusion protein fully functional in the ER lumen [20].

Analytical, diagnostic and therapeutic context of SEC63

• Cell fractionation and protease protection experiments confirm the prediction that Sec63p is an integral membrane protein [14].

References