Poster abstracts

Poster number 19 submitted by Bin Liu

Abnormal Ca2+ binding properties of the thin filaments caused by cardiomyopathy TnI mutations can be corrected through TnC mutagenesis

Bin Liu (The Ohio State University, Columbus, OH), Svetlana B. Tikunova (The Ohio State University, Columbus, OH), Jack A. Rall1 (The Ohio State University, Columbus, OH), Darl R. Swartz (Purdue University, West Lafayette, IN), Jonathan P. Davis (The Ohio State University, Columbus, OH)

Abstract:
The human restrictive cardiomyopathy mutation, TnIR192H, is associated with severe heart disease. In transgenic mice, the TnIR192H mutation sensitizes the heart to Ca2+ and causes diastolic dysfunction. We hypothesized that the impaired relaxation and increased Ca2+ sensitivity of the myofilaments was due to a slower rate of Ca2+ dissociation from TnC. At 15C, incorporation of TnIR192H into reconstituted thin filaments increased the Ca2+ sensitivity ~ 3.0-fold, and slowed the rate of Ca2+ dissociation ~1.4-fold. Since altered Ca2+ exchange properties may be one reason for the disease related dysfunction, we have designed TnC mutants with a vast range of Ca2+ dissociation rates and sensitivities to correct the abnormal Ca2+ binding properties caused by TnI cardiomyopathy mutations. Kinetically, two TnC mutants, TnCS69D and TnCT71D accelerated the rate of Ca2+ dissociation from TnC in thin filaments, ~2.4-and ~2.0-fold, respectively. Surprisingly, compared to wild-type TnC, TnCT71D had little effect on the Ca2+ sensitivity of the thin filaments, while TnCS69D desensitized ~4.0-fold the thin filaments to Ca2+. While TnCT71D had little effect on the increased Ca2+ sensitivity of the thin filaments caused by TnIR192H, it was able to correct the slower rate of Ca2+ dissociation to a rate similar to that of wild-type thin filaments. On the other hand, TnCS69D was able to correct the higher Ca2+ sensitivity caused by TnIR192H to a value similar to that of wild-type thin filaments. However, TnCS69D overcorrected the slower rate of Ca2+ dissociation from the thin filaments caused by TnIR192H by ~1.7-fold. Thus, the results indicate that an increased Ca2+ sensitivity of the thin filaments is not necessarily due to a slower Ca2+ dissociation rate. In conclusion, TnC mutagenesis can correct for the abnormal Ca2+ binding properties caused by the cardiomyopathy TnI mutations.

Keywords: Troponin, cardiomyopathy