SITE MAPPING AND MUCIN-TYPE O-GLYCAN PROFILING OF CD43 (LEUKOSIALIN / SIALOPHORIN) BY ELECTRON TRANSFER DISSOCIATION MASS SPECTROMETRY

摘要

Many of the mammalian clusters of differentiation (CD) antigens, which play crucial roles in immunological processes, carry mucin-type O-glycans (MTOG)[1]. MTOG imparts rigidity and large hydrodynamic volume to the polypeptide backbone and enables moderate reversible cis-interactions with neighbouring cell surface molecules. CD43 (leukosialin / sialophorin) is considered to be a negative regulator of immune activation. CD43 possesses an extended rod-like structure extending to 50 nm and is estimated to carry 80-90 MTOG on its polypeptide backbone[2]. Extracellular domain of CD43 consists of 234 amino acids including 93 (46 Ser and 47 Thr) potential MTOG sites. Studies on the MTOG structure of CD43 have been hampered due to its complexity and a vast number of theoretical proteoforms. Earlier studies by Schmid and co-workers on galactoglycoprotein (Galgp, the secreted form of CD43) had identified 25 occupied Ser/Thr sites using Edman degradation![3].