DESIGN AND SYNTHESIS OF POLYTRIPEPTIDE (LEUGLNPRO)N BASED UPON THE MATRIX PROTEIN AMELOGENIN

A linear neutral repetitive peptide, (Leu-Gln-Pro)n (n = 1-100), an an alog of the Ca2+ ion-binding domain of the matrix protein, amelogenin, has been synthesized. The polypeptide is mostly unordered in trifluor oethanol (TFE) at 25-degrees-C and its circular dichroism (CD) spectru m resembles that of the protein itself. In TFE the CD spectrum of (Leu -Gln-Pro)n reveals that the polypeptide interacts strongly with divale nt cations Mg2+, Ca2+, Sr2+, and Ba2+ accompanied by conformational re arrangement from a random to a more-ordered one. In the presence of Li +, Na+ and K+ ions no such conformational change has been observed. Th e CD curves of the complexes suggest the presence of type I beta-turns and reinforce the hypothesis that the region Gln112-Leu138 in ameloge nin is the Ca2+-binding domain. In the solid state, powder X-ray diffr action suggests that the polymeric (LQP)n may exist as isolated ''rigi d rods''.