1. Proinsulin C-peptide activates α-enolase: implications for C-peptide–cell membrane interaction
- Author
-
Keigo Fukano, Kohei Shimada, Kazuhiro Kimura, Yuko Okamatsu-Ogura, Tatsuya Ishii, Masayuki Saito, Toshihide Yoshida, Akihiro Kamikawa, and Akira Terao
- Subjects
Arginine ,Molecular Sequence Data ,HL-60 Cells ,Peptide ,Biology ,Biochemistry ,Cell membrane ,Cell surface receptor ,medicine ,Animals ,Humans ,Amino Acid Sequence ,Receptor ,Molecular Biology ,Cells, Cultured ,Proinsulin ,chemistry.chemical_classification ,Alanine ,Binding Sites ,C-Peptide ,Cell Membrane ,General Medicine ,Molecular biology ,medicine.anatomical_structure ,Membrane protein ,chemistry ,Phosphopyruvate Hydratase - Abstract
Proinsulin C-peptide shows beneficial effects on microvascular complications of Type 1 diabetes. However, the possible occurrence of membrane C-peptide receptor(s) has not been elucidated. The aim of this study was to identify and characterize membrane proteins to which C-peptide binds. The enzyme α-enolase was co-immunoprecipitated with C-peptide after chemical cross-linking to HL-60 cell surface proteins and identified by mass spectrometry. Recombinant α-enolase activity was modulated by C-peptide, with a significant decrease in K(m) for 2-phosphoglycerate without affecting V(max). The enzyme modulation by C-peptide was abolished when C-terminal basic lysine residue (K434) of the enzyme was replaced by neutral alanine or acidic glutamate, but not with basic arginine. The enzyme modulation by C-peptide was reproduced with the C-peptide fragments containing glutamate corresponding to position 27 (E27) of the full-length C-peptide. Addition of a lysine analogue to the assay and A31 cell culture abrogated the enzyme modulation and MAP kinase activation by C-peptide, respectively. The results indicate that C-peptide has the capacity to activate α-enolase through a specific interaction between E27 of the peptide and K434 of the enzyme. Since α-enolase plays a role as a cell surface receptor for plasminogen, it may conceivably also serve as a receptor for C-peptide in vivo.
- Published
- 2012