In vivo Mutant Screen as a Tool for Deciphering the Physiological Function of Leiomodin2 Domain

Dilated Cardiomyopathy (DCM) is a disease that has its roots in pathogenic mutations in sarcomeric proteins like Lmod2, an actin binding protein involved in regulating thin filament lengths in cardiac muscle. The physiological function of each of Lmod2 domains has yet to be studied. We found that introduction of a truncated form of Lmod2 lacking the tropomyosin binding site (TMBS), as well as introduction of Lmod2 lacking the third actin binding domain (ABS3) into the hearts of Lmod2 knock out (KO) mice via adeno-associated virus transduction results in shorter thin filament lengths for both mutants and altered heart morphology for the TMBS mutant. We also found that introduction of an actin binding site 2 mutant (ABS2) into Lmod2 KO hearts did not have an effect on thin filament lengths but cardiac morphology was affected. Based on our observation that introduction of Lmod2 ABS1 mutant into Lmod2 KO hearts resulted in longer thin filament lengths, we propose a novel function for Lmod2's actin binding site 1 (ABS1). We predict that this domain has capping activity. Overall this study provides us with 1) a novel function for ABS1; 2) new information about the function of each of Lmod2's domains; and 3) information on how mutations in these domains result in pathological molecular changes leading to disease.