Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 366, Issue 2, Pages 449-460Publisher
ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2006.10.026
Keywords
protein solubility; amino acid hydrophobicity; amino acid hydration; halophilic adaptation; beta-turn stability
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Funding
- NIGMS NIH HHS [GM-52483, R01 GM037039-20, R01 GM052483, T32 GM065088, R01 GM037039, R29 GM052483, GM-37039] Funding Source: Medline
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Poor protein solubility is a common problem in high-resolution structural studies, formulation of protein pharmaceuticals, and biochemical characterization of proteins. One popular strategy to improve protein solubility is to use site-directed mutagenesis to make hydrophobic to hydrophilic mutations on the protein surface. However, a systematic investigation of the relative contributions of all 20 amino acids to protein solubility has not been done. Here, 20 variants at the completely solvent-exposed position 76 of ribonuclease (RNase) Sa are made to compare the contributions of each amino acid. Stability measurements were also made for these variants, which occur at the i + 1 position of a type II beta-turn. Solubility measurements in ammonium sulfate solutions were made at high positive net charge, low net charge, and high negative net charge. Surprisingly, there was a wide range of contributions to protein solubility even among the hydrophilic amino acids. The results suggest that aspartic acid, glutamic acid, and serine contribute significantly more favorably than the other hydrophilic amino acids especially at high net charge. Therefore, to increase protein solubility, asparagine, glutamine, or threonine should be replaced with aspartic acid, glutamic acid or serine. (c) 2006 Elsevier Ltd. All rights reserved.
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