An alpha-actinin isoform which may cross-link intermediate filaments and microfilaments.

The G.3.5 antigen (named for the monoclonal antibody which recognizes it) has been characterized as an intermediate filament-associated protein found in a variety of tissue types, including human and rat astrocytes, rat skeletal and cardiac myocytes, fibroblasts, rat hepatocytes, and chicken and fish retinal tissues. Sequencing of proteolytic fragments indicated a high degree of similarity to alpha-actinin. Comparison of the G.3.5 antigen to alpha-actinin revealed that alpha-actinin and the G.3.5 antigen migrated similarly in reducing and non-reducing environments and had similar molecular masses (approximately 100,000). Overlay-immunoblotting assays indicated that the G.3.5 antigen and alpha-actinin could bind filamentous actin and desmin simultaneously. In contrast, immunocytochemistry indicated the G.3.5 antigen and alpha-actinin were immunologically distinct in tissue sections. The results of this study suggest that the G.3.5 antigen is an isoform of alpha-actinin which may serve to cross-link intermediate filaments to microfilaments, and that other isoforms of alpha-actinin may also share this property.