Kroczynska B, King-Simmons L, Alloza L, Alava MA, Elguindi EC, Blond SY. BIP co-chaperone MTJ1/ERDJ1 interacts with inter-α-trypsin inhibitor heavy chain 4.
Biochem Biophys Res Commun 2005;
338:1467-77. [PMID:
16271702 DOI:
10.1016/j.bbrc.2005.10.101]
[Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Accepted: 10/18/2005] [Indexed: 11/17/2022]
Abstract
MTJ1/ERdj1 and its human homologue HTJ1 are membrane proteins that interact with the molecular chaperone BiP through their J-domain. HTJ1 also contains a C-terminal cytosolic region of unknown function that consists of two SANT domains separated by a spacer region. We recently showed that the second SANT domain of HTJ1 (SANT2) binds to alpha1-antichymotrypsin and alters its serpin activity [B. Kroczynska, C.M. Evangelista, S.S. Samant, E.C. Elguindi, S.Y. Blond, The SANT2 domain of the murine tumor cell DnaJ-like protein 1 human homologue interacts with alpha1-antichymotrypsin and kinetically interferes with its serpin inhibitory activity, J. Biol. Chem. 279 (2004) 11432-11443]. Here, we identified a new variant of human inter-alpha-trypsin inhibitor heavy chain 4 (ITIH4) that also interacts with the SANT2 domain of HTJ1. Biochemical, mutagenesis, and fluorescence studies demonstrate that SANT2 binds to a carboxyl-terminal fragment that corresponds to the last third of the new ITIH4 isoform sequence (residues 588-930). ITIH4 and MTJ1 co-immunoprecipitate from total liver protein extracts and SANT2 protects the ITIH4(588-930) recombinant fragment from being processed by kallikrein in vitro. This work reveals that the SANT2 domain of HTJ1 is a genuine protein-protein interaction module.
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