ISSN:
1573-4919
Keywords:
calcium binding protein
;
TNBS
;
calreticulin
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Abstract The role of the primary amino groups of lysine sidechains in Ca2+ binding to calreticulin was evaluated by chemical modification of the amino group with 2,4,6-trinitrobenzenesulfonic acid (TNBS). TNBS binding to calreticulin could be described by two steps: (i) a fast reaction, with low affinity, and (ii) a slow reaction with a relatively high affinity. Inclusion of Ca2+ and/or Mg2+ decreased both the amount of TNBS bound to calreticulin and the apparent affinity constant of the slower reaction. In contrast, the properties of the faster reaction for TNBS binding were not sensitive to Ca2+ and/or Mg2+. Analysis of TNBS binding to the carboxyl-terminal (C-domain) and aminoterminal (N-domain) of calreticulin revealed that theC-domain andN-domain are responsible for the slow and fast component of the TNBS binding, respectively. In keeping with this, in the presence of Ca2+, TNBS binding to theC-domain was significantly reduced, whereas modification of theN-domain was unaffected. TNBS modification of calreticulin significantly decreased Ca2+ binding to the low affinity/high capacity Ca2+ binding site(s) which are localized to theC-domain but had no effect on the high affinity/low capacity Ca2+ binding localized to theN-domain. In theC-domain of calreticulin, which contains the low affinity/high capacity Ca2+ binding sites, acidic residues are interspersed at regular intervals with one or more positively charged lysine and arginine residues. Our results indicate that the aminogroups of the lysine sidechains in theC-domain of calreticulin have a role in the low affinity/high capacity Ca2+ binding that is characteristic of this region of the protein and which is proposed to contribute significantly to the capacity of the endoplasmic reticulum Ca2+ store. (Mol Cell Biochem130: 19–28, 1994)
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01084264
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