GRB2-SH3 (IMAGE) Center for Genomic Regulation Caption GRB2-SH3 is a protein with 34 amino acids, each which can be mutated into 19 different amino acids. This can result in 17 billion different combinations of the protein if only a single change allowed at each position. Credit Aina Martí Aranda/Wellcome Sanger Institute Usage Restrictions No restrictions. License CC0 Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.