Identification and characterization of novel variant major surface glycoprotein gene families in rat Pneumocystis carinii

The major surface glycoprotein (MSG) is an abundant, immunodominant protein on the surface of the opportunistic pathogen Pneumocystis carinii, The cur rent study identified two novel variant MSG (vMSG) gene families in rat I! carinii that are closely related to but distinct from MSG. These gene famil ies encode proteins of similar to 90 kDa (v1MSG) and similar to 115 kDa (v2 MSG). Compared with MSG, v1MSG is characterized by a deletion near the carb oxyl terminus, The predicted v1MSG and v2MSG proteins are highly homologous to MSG at the carboxyl, but not the amino, terminus, Like MSG, they are cy steine-rich, Approximately 10% of the apparent molecular weight is due to N -linked glycosylation, Southern blotting studies demonstrated that, like MS G, v1MSG and v2MSG are the products of multicopy gene families. However, un like MSG, each vMSG gene encodes a signal peptide, suggesting that the regu lation of vMSG is different from that of MSG.