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

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) greater than 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 alpha-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.