The present invention features novel binding molecules and methods of improving the specific binding affinity of binding molecules, which methods do not use X-ray crystallography. For example, in one aspect, the invention features methods of making antibodies with improved specific binding affinity for a polypeptide produced during prothrombin activation. The present invention is useful for a variety of applications including, e.g., producing binding molecules with improved binding affinity; and screening for binding molecules which are in low abundance.