Influence of L-cystinyl side-chain configurations on the melting of crosslinked alpha-tropomyosin dimers

The experimental melting profile reported by Holtzer, M.E., Holtzer, A. and Skolnick, J. (Macromolecules 16 (1983) 173-180) for the rabbit alpha-tropomyosin dimer crosslinked at cysteine residue 190 has been analyzed using matrix methods. The configuration partition function employed includes a term arising from interactions at the crosslink site. This term, denoted by omega, is found to be smaller than 1, implying that events at the crosslink site resist helix formation by dimer. A theoretical analysis of the conformational restrictions imposed on the crosslink provides a satisfactory estimate of omega at high temperatures. Agreement deteriorates at lower temperatures, perhaps as a consequence of difficulty in establishing a reliable value for omega from analysis of the low-temperature circular dichroism data.