G35 Antigen Appears to be a Form of [Alpha]-actinin which Co-isolates and Co-localizes with Type III Intermediate Filaments
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The G3.5 monoclonal antibody (mAB) was raised against multiple sclerotic plaque material from human brain and spinal cord. The antigen of this antibody has been previously designated an a-actinin-like protein with the unusual features of localizing separately from skeletal muscle a-actinin, localizing with desmin in muscle Mid with GFAP in astrocytes, and simultaneously binding actin and desmin in vitro. The physical properties of the antigen are essentially identical to the published properties of a-actinin, and initial amino acid sequencing showed a high degree of identity to isoform 2 of the a-actinin family except for three deviant amino acids. Attempts to use amino acid sequence data to isolate a unique gene sequence for the G3.5 antigen have failed. Recent studies have demonstrated that a-actinin has a more complex role in cellular structure and development than previously thought. a-Actinin has been shown to be subject to tyrosine kinase phosphorylation and associate with many proteins in addition to actin, including intermediate filaments. Because of this new information, we reisolated the G3.5 antigen from rat skeletal muscle as before, using a modified desmin isolation protocol. The G3.5 antigen was then released and separated from the insoluble desmin fraction by addition of a reducing agent and centrifugation. Limited proteolysis and sequencing of the G3.5 antigen has provided 7 fragments totaling 72 residues, which share a high degree of identity in primary sequence to regions found in rat a-actinins. Immunohistochemical analysis of the G3.5 antigen was also performed, producing results that suggest some co-localization of the G3.5 mAB and anti-a-actinin antibodies while areas of separate localization are also present. The preponderance of evidence therefore suggests that mAB G3.5 reccognizes a-actinin, and ascribes to a-actinin the novel function of associating with type III intermediate filaments as well as actin. The source of a deviant sequence motif remains unresolved.
CitationAbedi, A. (2006). G35 antigen appears to be a form of [Alpha]-actinin which co-isolates and co-localizes with type III intermediate filaments (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.
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