It is here claimed an oligopeptide of sequence SJXXZGXP (SEQ ID no. 7), where S is a serine, J is a serine or it is absent, X is independently any desired amino acid, Z is selected from tyrosine, histidine, phenylalanine or tryptophan, G is a glycine and P is a proline, characterized by the fact that at least the residue Z is substituted with at least one halogen atom selected from Br, Cl, I. In a further embodiment, the use of the described oligopeptide and of fibers obtained from the same, having rigid and elastomeric properties, are claimed.