The essential light chain N-terminal extension alters force and fiber kinetics in mouse cardiac muscle.
The functional significance of the actin-binding region at the N terminus of the cardiac myosin essential light chain (ELC) remains elusive. In a previous experiment, the endogenous ventricular ELC was replaced with a protein containing a 10-amino acid deletion at positions 5-14 (ELC1vDelta5-14, referred to as 1vDelta5-14), a region that interacts with actin. 1vDelta5-14 mice showed no discernable mutant phenotype in skinned ventricular strips. However, because the myofilament lattice swells upon skinning, the mutant phenotype may have been concealed by the inability of the ELC to reach the actin-binding site. Using the same mouse model, we repeated earlier measurements and performed additional experiments on skinned strips osmotically compressed to the intact lattice spacing as determined by x-ray diffraction. 1vDelta5-14 mice exhibited decreased maximum isometric tension without a change in calcium sensitivity. The decreased force was most evident in 5-6-month-old mice compared with 13-15-month-old mice and may account for the greater ventricular wall thickness in young 1vDelta5-14 mice compared with age-matched controls. No differences were observed in unloaded shortening velocity at maximum calcium activation. However, 1vDelta5-14 mice exhibited a significant difference in the frequency at which minimum complex modulus amplitude occurred, indicating a change in cross-bridge kinetics. We hypothesize that the ELC N-terminal extension interaction with actin inhibits the reversal of the power stroke, thereby increasing isometric force. Our results strongly suggest that an interaction between residues 5-14 of the ELC N terminus and the C-terminal residues of actin enhances cardiac performance.
Miller
Mark S
MS
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, Vermont 05405, USA. mmiller@cems.uvm.edu
Palmer
Bradley M
BM
Ruch
Stuart
S
Martin
Lisa A
LA
Farman
Gerrie P
GP
Wang
Yuan
Y
Robbins
Jeffrey
J
Irving
Thomas C
TC
Maughan
David W
DW
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000737:chemistry; D000818:Animals; D001665:Binding Sites; D001835:Body Weight; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D003911:Dextrans / Q000494:pharmacology; D004452:Echocardiography; D017353:Gene Deletion; D006801:Humans; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D008956:Models, Chemical; D009154:Mutation; D009206:Myocardium / Q000378:metabolism / Q000473:pathology*; D018995:Myosin Heavy Chains / Q000378:metabolism; D009995:Osmosis; D010641:Phenotype; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D014961:X-Ray Diffraction
D000199:Actins; D003911:Dextrans; D020033:Protein Isoforms; D018995:Myosin Heavy Chains; D002118:Calcium