Programmed Cleavage at Proline: Application to the Sequence Determination of Wheat Storage Proteins

Abstract

Our observation that proline was only partially cleaved when using the protein sequenator (1) for amino acid sequencing of wheat storage proteins led us to study cleavage at proline. These proteins are notable for their high proline (~20%) and glutamine (~ 40%) contents, and repeating sequences including recurrent combinations of the type -X-Pro-X- where X is frequently Gln, less frequently, Tyr or Phe, and sometimes other amino acids (2, 3). Sequencing of these proteins was complicated by partial cleavages at proline residues that resulted in overlap and rapidly increasing background. Attempts to prevent this problem by the use of higher temperatures (4) in the reaction chamber and double cleavage at proline were insufficient to overcome the problem. As part of a continuing sequencing effort, we have used manual Edman sequencing to determine those conditions that provide for complete cleavage at proline.