Title : Primary structure of human
alpha 2-macroglobulin
Abstract :
- V
- The complete structure
- The primary structure of the tetrameric plasma glycoprotein human alpha 2-macroglobulin has been determined
- The identical subunits contain 1451 amino acid residues
- Glucosamine-based oligosaccharide groups are attached to asparagine residues 32, 47, 224, 373, 387, 846, 968, and 1401
- Eleven intra chain disulfide bridges have been placed (Cys25-Cys63, Cys228-Cys276, Cys246-Cys264, Cys255-Cys408, Cys572-Cys748, Cys619-Cys666, Cys798-Cys826, Cys824-Cys860, Cys898-Cys1298, Cys1056-Cys1104, and Cys1329-Cys1444)
- Cys-447 probably forms an inter chain bridge with Cys-447 from another subunit
- The beta-SH group of Cys-949 is thiol esterified to the gamma-carbonyl group of Glx-952, thus forming an activatable reactive site which can mediate covalent binding of nucleophiles
- A putative transglutaminase cross-linking site is constituted by Gln-670 and Gln-671
- The primary sites of proteolytic cleavage in the activation cleavage area (the "bait" region ) are located in the sequence: -Arg681-Val-Gly-Phe-Tyr-Glu-
- The molecular weight of the unmodified alpha 2-macroglobulin subunit is 160,837 and approximately 179,000, including the carbohydrate groups
- The presence of possible internal homologies within the alpha 2-macroglobulin subunit is discussed
- A comparison of stretches of sequences from alpha 2-macroglobulin with partial sequence data for complement components C3 and C4 indicates that these proteins are evolutionary related
- The properties of alpha 2-macroglobulin are discussed within the context of proteolytically regulated systems with particular reference to the complement components C3 and C4