Structure of the band 3 transmembrane domain.

The N-glycosylated membrane domain of band 3 consists of multiple membrane spanning segments that come together to form a regulated transmembrane passage for the exchange of anions. In this article we review the structural features of the membrane domain of band 3. Electron microscopic analysis of 2-dimensional crystals have confirmed the dimeric nature of the protein and has provided the overall shape of the membrane domain. The high degree of sequence identity in the transmembrane segments, and the finding that these segments are helical and remain tightly associated after proteolytic cleavage of the connecting loops, suggests that the interactions between transmembrane helices are specific 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 cell diseases (HEMPAS and SAO) that affect the band 3 oligosaccharide structure and other properties of the protein are the subject of continued studies.