1UCL

Mutants of RNase Sa

Summary for 1UCL

• Entry DOI: 10.2210/pdb1ucl/pdb
• Related: 1RGG 1UCI 1UCJ 1UCK
• Descriptor: Guanyl-specific ribonuclease Sa, SULFATE ION (3 entities in total)
• Functional Keywords: protein stability, hydrogen bond, burial polar, hydrolase
• Biological source: Streptomyces aureofaciens
• Cellular location: Secreted: P05798
• Total number of polymer chains: 2
• Total formula weight: 21264.99

Authors

Takano, K.,Scholtz, J.M.,Sacchettini, J.C.,Pace, C.N. (deposition date: 2003-04-15, release date: 2003-09-09, Last modification date: 2023-12-27)

Primary citation

Takano, K.,Scholtz, J.M.,Sacchettini, J.C.,Pace, C.N.
The contribution of polar group burial to protein stability is strongly context-dependent
J.Biol.Chem., 278:31790-31795, 2003

PubMed Abstract: We previously suggested that proteins gain more stability from the burial and hydrogen bonding of polar groups than from the burial of nonpolar groups (Pace, C. N. (2001) Biochemistry 40, 310-313). To study this further, we prepared eight Thr-to-Val mutants of RNase Sa, four in which the Thr side chain is hydrogen-bonded and four in which it is not. We measured the stability of these mutants by analyzing their thermal denaturation curves. The four hydrogen-bonded Thr side chains contribute 1.3 +/- 0.9 kcal/mol to the stability; those that are not still contribute 0.4 +/- 0.9 kcal/mol to the stability. For 40 Thr-to-Val mutants of 11 proteins, the average decrease in stability is 1.0 +/- 1.0 kcal/mol when the Thr side chain is hydrogen-bonded and 0.0 +/- 0.5 kcal/mol when it is not. This is clear evidence that hydrogen bonds contribute favorably to protein stability. In addition, we prepared four Val-to-Thr mutants of RNase Sa, measured their stability, and determined their crystal structures. In all cases, the mutants are less stable than the wild-type protein, with the decreases in stability ranging from 0.5 to 4.4 kcal/mol. For 41 Val-to-Thr mutants of 11 proteins, the average decrease in stability is 1.8 +/- 1.3 kcal/mol and is unfavorable for 40 of 41 mutants. This shows that placing an [bond]OH group at a site designed for a [bond]CH3 group is very unfavorable. So, [bond]OH groups can contribute favorably to protein stability, even if they are not hydrogen-bonded, if the site was selected for an [bond]OH group, but they will make an unfavorable contribution to stability, even if they are hydrogen-bonded, when they are placed at a site selected for a [bond]CH3 group. The contribution that polar groups make to protein stability depends strongly on their environment.

PubMed: 12799387
DOI: 10.1074/jbc.M304177200

Experimental method

X-RAY DIFFRACTION (1.82 Å)