Identification of a heparin binding domain in the N-terminal cleavage site of pro-islet amyloid polypeptide. Implications for islet amyloid formation.
Islet amyloid deposits are a characteristic pathologic lesion of the pancreas in type 2 diabetes and are composed primarily of the islet beta cell peptide islet amyloid polypeptide (IAPP or amylin) as well as the basement membrane heparan sulfate proteoglycan perlecan. Impaired processing of the IAPP precursor has been implicated in the mechanism of islet amyloid formation. The N- and C-terminal cleavage sites where pro-IAPP is processed by prohormone convertases contain a series of basic amino acid residues that we hypothesized may interact with heparan sulfate proteoglycans. This possibility was tested using affinity chromatography by applying synthetic fragments of pro-IAPP to heparin-agarose and heparan sulfate-Sepharose. An N-terminal human pro-IAPP fragment (residues 1-30) was retained by both heparin-agarose and heparan sulfate-Sepharose, eluting at 0.18 m NaCl at pH 7.5. Substitution of alanine residues for two basic residues in the N-terminal cleavage site abolished heparin and heparan sulfate binding activity. At pH 5.5, the affinity of the wild-type peptide for heparin/heparan sulfate was increased, implying a role for histidine residues at positions 6 and 28 of pro-IAPP. A C-terminal pro-IAPP fragment (residues 41-67) had no specific affinity for either heparin or heparan sulfate, and the N- or C-terminal fragments had only weak affinity for chondroitin sulfate. These data suggest that monomeric N-terminal human pro-IAPP contains a heparin binding domain that is lost during normal processing of pro-IAPP.
Park
K
K
Department of Pathology and Laboratory Medicine and the British Columbia Research Institute for Children's and Women's Health, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada.
Verchere
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CB
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000682:Amyloid / Q000096:biosynthesis* / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002809:Chondroitin Sulfates / Q000378:metabolism; D002846:Chromatography, Affinity; D006493:Heparin / Q000378:metabolism*; D006497:Heparan Sulfate; D006801:Humans; D058228:Islet Amyloid Polypeptide; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D000682:Amyloid; D002809:Chondroitin Sulfates; D006493:Heparin; D006497:Heparan Sulfate; D058228:Islet Amyloid Polypeptide; D010446:Peptide Fragments; D011994:Recombinant Proteins; C422904:pro-islet amyloid polypeptide