EXPLORING LEIOMODIN'S C-TERMINAL EXTENSION AND ITS ROLE IN THIN FILAMENT BINDING - ABSTRACT WITHIN CARDIAC AND SKELETAL MUSCLE CELLS, CONTRACTILE SUBUNITS CALLED SARCOMERES ARE MADE UP OF THICK AND THIN FILAMENTS. THE FILAMENTS SLIDE AGAINST ONE ANOTHER, CONTRACTING THE MUSCLE FOR EVERYDAY USE. TO MAINTAIN PROPER FUNCTION OF THE MUSCLE, THE ORGANIZATION AND MECHANICS OF THE PROTEINS THAT MAKE UP THE SARCOMERE MUST BE TIGHTLY REGULATED. LEIOMODIN (LMOD) ACTS AS A LENGTH PROMOTER AT THE POINTED END OF THE THIN FILAMENT MAKING IT A KEY PLAYER IN FORCE-LENGTH RELATED REGULATION. RECENTLY, IT WAS FOUND THAT LMOD CONTAINS ADDITIONAL LATERAL ACTIN BINDING REGIONS (L-ABRS) IN ITS C-TERMINAL EXTENSION. THIS ALLOWS LMOD THE ABILITY TO BIND THE SIDES OF THIN FILAMENTS BY BINDING TO EXPOSED ACTIN PROTOMERS NEAR THE THIN FILAMENT POINTED END. IT IS KNOWN THAT LMOD2'S C- TERMINAL EXTENSION IS BIOLOGICALLY RELEVANT TO HUMAN HEALTH AS NATURAL HUMAN MUTATIONS HAVE LED TO THE DEVELOPMENT OF DILATED CARDIOMYOPATHY. CRYO-EM DATA SHOWS LMOD2, THE CARDIAC ISOFORM OF LMOD, BINDS TO POSITIVELY CHARGED REGIONS ALONG THE THIN FILAMENT THAT COINCIDES WITH CROSS BRIDGE BINDING SITES. TO EXPLAIN EFFECTS OF THE CARDIOMYOPATHY-RELATED MUTATIONS, THE ROLE AND MOLECULAR MECHANISMS OF THE TF SIDE BINDING SHOULD BE UNDERSTOOD. IN THIS PROJECT, I WILL SOLVE THE STRUCTURE OF THE BINDING INTERFACE BETWEEN LMOD2 AND F-ACTIN AND I TEST THE HYPOTHESIS THAT LMOD2 CAN INHIBIT ACTOMYOSIN INTERACTIONS NEAR THE POINTED END OF TFS, PROTECTING THE POINTED END FROM CROSS-BRIDGE CYCLING. IN ADDITION, IN THIS STUDY, WE WILL DEVELOP A METHOD USING NMR AND MDS THAT CAN BE ADAPTED TO OTHER INTRINSICALLY DISORDERED PROTEINS IN COMPLEX WITH LARGE PROTEIN ASSEMBLIES.