Characterization of four G_O‐type proteins purified from bovine brain membranes

Abstract

Recently we reported there were at least four types of G O or G0-1ike proteins in bovine brain membranes based on their elution profiles from Mono Q columns and their immunological reactivities; one of the proteins was purified as an ct-monomeric form, and the others as ~flT-trimers. The four proteins, of which ct-subunits were confirmed to be a family of Go-type by an immunoblot analysis, were thus referred to as %1, Go2, G03 and G04, respectively, in order of their elutions from the column. Immunostained peptide mappings arising from proteolytic digestions of the four ctsubunits, together with their fragmentation patterns containing radiolabeled ADP-ribose that had been incorporated by pertussis toxin-catalyzed ADP-ribosylation, suggested that the four G0-c~ were classified into either of two groups such as %1 and G02-c~ or Go3-C~ and Go4-C~. The kinetic parameters of their GTPase activities, however, revealed that there were different properties between %1 and Go2-c~ or Go3-c~ and Go4-a. Thus, the four G0-type proteins appeared to be different entities from one another.GTP-binding protein; Pertussis toxin (IAP); GTPase activity

Heterogeneity of three electrophoretically distinct Go α‐subunits in mammalian brain

“…All membranes obtained from whole brain tissue but not membranes from distinct cell lines tested show a third Goe,-protein with a pl value of about 5.45 which is detected by 0~o~-and ~o.~,,~o,-specific antibodies but not by ~o2-specific antibodies. The most acidic ~to-forrn on 2D-SDS-PAGE and the slowest migrating a,, protein on urea-containing SDS-PAGE is identical with neither the two :to2 nor two ~oj isoforms reported previously [10,11]. Therefore, it is not Gag* described by Goldsmith etal.…”

“…Purification of the corresponding proteins revealed the existence of two isoforms of each :¢oj and :to,. [8][9][10][11]. Additionally, a third ~o form was detected in brain membranes, using specific antibodies [12][13][14][15].…”

“…All three ~o proteins appear as 2 isoforms in two different gel systems. Since myristoylation slightly changes the mobility of cto proteins in urea-containing SDS-PAGE [19], it is feasible that the two isoforms of the proteins found in this study, by Katada's group [10,11], and Goldsmith et al [8] differ in their co-or posttranslational modifications. Experiments are un.…”

“…So far three splice variants of the ~,,-gene coding for two Cto proteins have been identified by molecular cloning [4][5][6][7]. Interestingly, purification of the two splice variants revealed the existence of two isoforms of each ~Xot and ~o2 [8][9][10][11]. Recently, several groups reported on a third form of ao in brain membranes, using urea-containing SDS-PAGE gels [12][13][14][15].…”

Characterization of the Major Bovine Brain Go α Isoforms

“…Three of the isoforms, ␣ oA , ␣ oB , and ␣ oC , are purified associated with ␤␥ dimers as G oA , G oB , and G oC , while ␣ oD , an inconsistently observed ␣ o isoform, is not. Immunological evidence and peptide mapping suggest that ␣ oB and ␣ oD are protein products of the ␣ o2 mRNA, whereas ␣ oA and ␣ oC are translated from the ␣ o1 mRNA (23)(24)(25)(26). The functional significance of these different ␣ o isoforms is not yet clear, but the G oA , G oB , and G oC heterotrimers each contain a different assortment of ␤␥ dimers (23).…”