The interaction of rabbit skeletal muscle troponin-T fragments with troponin-I

Abstract

The interactions of troponin-I (Tn-I) with a variety of fragments spanning the length of the troponin-T (Tn-T) polypeptide chain have been reinvestigated at physiological ionic strength by affinity chromatographic, gel filtration, and circular dichroism methodologies. Strong binding was observed with fragment T2 (residues 159–259) mimicking that observed with whole Tn-T and Tn-I. Partial binding was seen with the shorter cyanogen bromide (CB) fragments of Tn-T in the order CB4 (residues 176–230) > CB6 (residues 239–259) or CB5 (residues 152–175). No interaction with Tn-I was observed with fragments (CB2, CB3, T1) encompassing residues 1–158 of Tn-T. Based on the present results and the work of others, the binding region for Tn-I includes residues 159–259 and perhaps extends into the highly helical CB2 region (residues 71–151) of Tn-T. No evidence has been obtained by ourselves or others for the interaction of the CB3 region (1–70) with Tn-I. A significant increase (11.6%) in α-helical content was observed when an equimolar amount of fragment T2 (residues 159–259) was mixed with Tn-I, a result similar to that seen with whole Tn-T and Tn-I.