Identification of the major casein kinase I phosphorylation sites on
erythrocyte band 3
CC Wang, M Tao, T Wei and PS Low
Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA.
Human erythrocyte band 3 is a major substrate of two red blood cell protein
kinases, casein kinase I and p72syk protein tyrosine kinase. Although the
phosphorylation sites and physiologic consequences of p72syk
phosphorylation have been characterized, little is known regarding casein
kinase I phosphorylation. In this report, we identify the major
phosphorylation site of casein kinase I. Using isolated components, casein
kinase I was found to phosphorylate the cytoplasmic domain of band 3
(CDB3), primarily on Thr residues. Classical peptide mapping narrowed the
major phosphorylation site to a peptide encompassing residues 24-91.
Computer-assisted evaluation of this sequence not only showed two consensus
casein kinase I phosphorylation sites, but also provided information on how
to proteolytically separate and isolate the candidate sites. Following the
suggested protocols, a heptapeptide containing the major phosphorylation
site was isolated, subjected to amino acid sequencing, and found to be
phosphorylated on Thr 42. A minor phosphorylation site was similarly
identified as Ser 303. Because Thr 42 is situated near the binding sites on
CDB3 of ankyrin, protein 4.1, protein 4.2, and the glycolytic enzymes,
phosphorylation of CDB3 by casein kinase I could conceivably impact
erythrocyte structure and/or function.
Volume 89,
Issue 8,
pp. 3019-3024,
04/15/1997
Copyright © 1997 by The American Society of Hematology
