title: The sucrase-isomaltase complex: primary structure, membrane-orientation, and evolution of a stalked, intrinsic brush border protein.
abstract: The complete primary structure (1827 amino acids) of rabbit intestinal pro-sucrase-isomaltase (pro-SI) was deduced from the sequence of a nearly full-length cDNA. Pro-SI is anchored in the membrane by a single 20 amino acid segment spanning the bilayer only once. The amino-terminal, cytoplasmic domain consists of 12 amino acids and is not preceded by a cleaved leader sequence. This suggests a dual role for the membrane-spanning segment as an uncleaved signal for membrane insertion. This is followed by a 22 residue serine/threonine-rich, probably glycosylated, stretch, presumably forming the stalk on which the globular, catalytic domains are directed into the intestinal lumen. Following this is a high degree of homology between the isomaltase and sucrase portions (41% amino acid identity), indicating that pro-SI evolved by partial gene duplication.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002462:Cell Membrane / Q000032:analysis / Q000378:metabolism; D004247:DNA / Q000302:isolation & purification; D005796:Genes; D007413:Intestinal Mucosa / Q000378:metabolism; D008565:Membrane Proteins / Q000302:isolation & purification*; D008871:Microvilli / Q000032:analysis / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000302:isolation & purification*; D011499:Protein Processing, Post-Translational; D011817:Rabbits; D013394:Sucrase-Isomaltase Complex / Q000235:genetics / Q000302:isolation & purification*
chemical_list: D008565:Membrane Proteins; D009097:Multienzyme Complexes; D004247:DNA; D013394:Sucrase-Isomaltase Complex