ISOFORM CLONING, ACTIN-BINDING, AND CHROMOSOMAL LOCALIZATION OF HUMAN ERYTHROID DEMATIN, A MEMBER OF THE VILLIN SUPERFAMILY

Dematin is an actin-bundling protein of the erythroid membrane skeleton and is abundantly expressed in human brain, heart, skeletal muscle, kidney, and lung. The 48-kDa subunit of dematin contains a headpiece domain which was originally identified in villin, an actin-binding protein of the brush-border cytoskeleton. The headpiece domain of villin is essential for its morphogenic function in vivo. Here we report the primary structure of 52-kDa subunit of dematin which differs from the 48-kDa subunit by a 22-amino-acid insertion within its headpiece domain. A unique feature of the insertion sequence of the 52-kDa subunit is its homology to erythrocyte protein 4.2. The insertion sequence also includes a cysteine residue which may explain the formation of sulfhydryl-linked trimers of dematin. Actin binding measurements using recombinant fusion proteins re vealed that each monomer of dematin contains two Factin binding sites: one in the headpiece domain and the other in the undefined N-terminal domain. Although the actin bundling activity of intact dematin was abolished by phosphorylation, no effect of phosphorylation was observed on the actin binding activity of fusion proteins. Using somatic cell hybrid panels and fluorescence in situ hybridization, the dematin gene was localized on the short arm of chromosome 8. The dematin locus, 8p21.1, is distal to the known locus of human erythroid ankyrin (8p11.2) and may contribute to the etiology of hemolytic anemia in a subset of patients with severe hereditary spherocytosis.