The invention provides an isolated nucleic acid encoding a water-soluble polypeptide fragment of human tryptophanyl-tRNA synthetase, which is useful for the inhibition of angiogenesis. The nucleic acid comprises a polynucleotide of SEQ ID NO: 6, a polynucleotide hybridizable to SEQ ID NO: 6, a polynucleotide that encodes the polypeptide of SEQ ID NO: 7, a polynucleotide that encodes a polypeptide of SEQ ID NO: 12, a polynucleotide that encodes a polypeptide epitope of SEQ ID NO: 7, or a polynucleotide that is hybridizable to a polynucleotide that encodes a polypeptide epitope of SEQ ID NO: 7. Vectors and recombinant cells comprising the nucleic acid are also provided.