The present application relates to isolated amino acid sequence comprising multiple repeats of a semi-synthetic spider silk protein domain, or any functional homolog, variant, derivative, fragment or mutant thereof. The amino acid sequence of the invention further comprises an N-terminal region and a C-terminal region. The invention further provides a nucleic acid encoding the amino acid sequence of the invention, an expression vector comprising said nucleic acid, a host cell transformed with said expression vector, a recombinant spider silk protein thus produced and a fiber composed of the recombinant spider silk protein. The invention further encompasses a composition comprising as an active ingredient said amino acid sequence or any said recombinant protein or fiber comprising the same. Lastly, the invention relates to an article comprising at least one fiber composed of said recombinant spider silk protein.
