BIP co-chaperone MTJ1/ERDJ1 interacts with inter-α-trypsin inhibitor heavy chain 4

Barbara Kroczynska, LaShaunda King-Simmons, Leonor Alloza, Maria A. Alava, Ebrahim C. Elguindi, Sylvie Y. Blond*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


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 α1-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 α1-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-α-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 ITIH4588-930 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.

Original languageEnglish (US)
Pages (from-to)1467-1477
Number of pages11
JournalBiochemical and Biophysical Research Communications
Issue number3
StatePublished - Dec 23 2005


  • Acute phase proteins
  • BiP
  • ITIH4
  • Kallikrein
  • MTJ1
  • Molecular chaperones
  • SANT domain
  • Tryptophan fluorescence
  • Yeast two-hybrid

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology

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