Thymidylate synthase (TS),an essential enzyme for catalyzing the biosynthesisof thymidylate,is a critical therapeutic target in cancer therapy.Recent studies have shown that TSfunctions as an RNA-binding protein by interacting with two different sequences on its ownmRNA,thus,repressing translational efficiency.In this study,peptides binding TS RNA with highaffinity were isolated using mRNA display from a large peptide library (>10^(13) differentsequences).The randomized library was subjected up to twelve rounds of in vitro selection andamplification.Comparing the amino acid composition of the selected peptides (12th round,R12) withthose from the initial random library (round zero,R0),the basic and aromatic residues in theselected peptides were enriched significantly,suggesting that these peptide regions might beimportant in the peptide-TS mRNA interaction.Categorizing the amino acids at each random positionbased on their physicochemical properties and comparing the distributions with those of the initialrandom pool,an obvious basic charge characteristic was found at positions 1,12,17 and 18,suggestingthat basic side chains participate in RNA binding.Secondary structure prediction showed that theselected peptides of R12 pool represented a helical propensity compared with R0 pool,and the regionswere rich in basic residues.The electrophoretic gel mobility shift and in vitro translation assaysshowed that the peptides selected using mRNA display could bind TS RNA specifically and inhibit thetranslation of TS mRNA.Our results suggested that the identified peptides could be used as new TSinhibitors and developed to a novel class of anticancer agents.
YAN Song1,2, NIU RongLi2, WANG Zheng2 & LIN XiuKun2 1 School of Environmental Science and Engineering, Dalian Jiaotong University, Dalian 116028, China
