STRUCTURE OF THE BAND-3 TRANSMEMBRANE DOMAIN

The N-glycosylated membrane domain of band 3 consists of multiple memb rane spanning segments that come together to form a regulated transmem brane passage for the exchange of anions. In this article we review th e structural features of the membrane domain of band 3. Electron micro scopic analysis of 2-dimensional crystals have confirmed the dimeric n ature of the protein and has provided the overall shape of the membran e domain. The high degree of sequence identity in the transmembrane se gments, and the finding that these segments are helical and remain tig htly associated after proteolytic cleavage of the connecting loops, su ggests that the interactions between transmembrane helices are specifi c and form the foundation for the structure of the membrane domain. N- glycosylation of band 3 is not essential for the transport function of the protein. N-glycosylation mutagenesis indicates that band 3 can be glycosylated on multiple loops and spans the membrane 12 times. Red c ell diseases (HEMPAS and SAG) that affect the band 3 oligosaccharide s tructure and other properties of the protein are the subject of contin ued studies.