Contribution of each amino acid residue to the dual effects of a synthetic peptide of actin binding region of heat shock protein 20 on the contraction of skinned smooth muscles

Abstract

Heat shock protein 20 (HSP20) has actin binding capacity and its amino acid sequence of actin binding region (residues 110-121; GFVAREFHRRYR) is highly homogenous to the inhibitory region of skeletal muscle troponin I (residues 104-115). Our previous study showed that, in Titon-X-100 skinned muscle preparations from guinea pig taenia caeci, a synthetic peptide of the actin binding region of HSP20 (HSP20_p) had both a suppressing effect on the maximal Ca²⁺ induced force and an enhancing effect on the Ca²⁺ sensitivity for the force (Yoshino et al., ). In the present study, to evaluate the contribution of each amino acid residue of HSP20_p to the dual effects of HSP20_p on the skinned taenia, we compared the effects of 11 HSP20_p analogues, which consisted of single glycine replacement, on the Ca²⁺-induced contraction. Every residue of HSP20_p was necessary to achieve maximum inhibition of the Ca²⁺-induced contraction. On the other hand, replacing F111, V112, A113, E115, F116 or R121 for glycine resulted in losing enhancing effects on the Ca²⁺ sensitivity for the force. These results suggest that, in phasic smooth muscles, the pathways through which HSP20_p modulated the maximal Ca²⁺ induced force and Ca²⁺ sensitivity for the force appears to be different. [J Physiol Sci. 2006;56 Suppl:S143]