Asp79 makes a large, unfavorable contribution to the stability of RNase Sa.


Abstract

The two most buried carboxyl groups in ribonuclease Sa (RNase Sa) are Asp33 (99% buried; pK 2.4) and Asp79 (85% buried; pK 7.4). Above these pK values, the stability of the D33A variant is 6kcal/mol less than wild-type RNase Sa, and the stability of the D79A variant is 3.3kcal/mol greater than wild-type RNase Sa. The key structural difference between the carboxyl groups is that Asp33 forms three intramolecular hydrogen bonds, and Asp79 forms no intramolecular hydrogen bond. Here, we focus on Asp79 and describe studies of 11 Asp79 variants. Most of the variants were at least 2kcal/mol more stable than wild-type RNase Sa, and the most interesting was D79F. At pH 3, below the pK of Asp79, RNase Sa is 0.3kcal/mol more stable than the D79F variant. At pH 8.5, above the pK of Asp79, RNase Sa is 3.7kcal/mol less stable than the D79F variant. The unfavorable contribution of Asp79 to the stability appears to result from the Born self-energy of burying the charge and, more importantly, from unfavorable charge-charge interactions. To counteract the effect of the negative charge on Asp79, we prepared the Q94K variant and the crystal structure showed that the amino group of the Lys formed a hydrogen-bonded ion pair (distance, 2.71A; angle, 100 degrees ) with the carboxyl group of Asp79. The stability of the Q94K variant was about the same as the wild-type at pH 3, where Asp79 is uncharged, but 1kcal/mol greater than that of wild-type RNase Sa at pH 8.5, where Asp79 is charged. Differences in hydrophobicity, steric strain, Born self-energy, and electrostatic interactions all appear to contribute to the range of stabilities observed in the variants. When it is possible, replacing buried, non-hydrogen bonded, ionizable side-chains with non-polar side-chains is an excellent means of increasing protein stability. Study holds ProTherm entries: 19007, 19008, 19009, 19010, 19011, 19012, 19013, 19014, 19015, 19016, 19017, 19018, 19019, 19020, 19021, 19022, 19023, 19024, 19025, 19026, 19027, 19028, 19029, 19030, 19031, 19032, 19033, 19034, 19035, 19036, 19037, 19038, 19039, 19040, 19041, 19042, 19043, 19044, 19045, 19046, 19047, 19048, 19049, 19050, 19051, 19052, 19053, 19054, 19055, 19056, 19057, 19058, 19059, 19060, 19061, 19062 Extra Details: protein stability; buried carboxyl group; pK; hydrogen bonds; ion pair

Submission Details

ID: KJMRYGXK3

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:51 p.m.

Version: 1

Publication Details
Trevino SR;Gokulan K;Newsom S;Thurlkill RL;Shaw KL;Mitkevich VA;Makarov AA;Sacchettini JC;Scholtz JM;Pace CN,J. Mol. Biol. (2005) Asp79 makes a large, unfavorable contribution to the stability of RNase Sa. PMID:16288913
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P
 

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)


Relevant PDB Entries

Structure ID Release Date Resolution Structure Title
1C54 2001-11-28 SOLUTION STRUCTURE OF RIBONUCLEASE SA
1LNI 2002-07-31 1.0 CRYSTAL STRUCTURE ANALYSIS OF A RIBONUCLEASE FROM STREPTOMYCES AUREOFACIENS AT ATOMIC RESOLUTION (1.0 A)
1T2H 2004-12-21 1.0 Y81W mutant of RNase Sa from Streptomyces aureofaciens
4GHO 2013-08-14 1.1 Crystal Structure Analysis of Streptomyces aureofaciens Ribonuclease S24A mutant
1T2I 2004-12-21 1.1 T76W mutant of RNase Sa from Streptomyces aureofaciens
1ZGX 2006-08-08 1.13 Crystal structure of ribonuclease mutant
1RGE 1996-10-14 1.15 HYDROLASE, GUANYLORIBONUCLEASE
1YNV 2005-07-19 1.2 Asp79 makes a large, unfavorable contribution to the stability of RNase Sa
1RGG 1996-10-14 1.2 HYDROLASE, GUANYLORIBONUCLEASE
1RGH 1996-10-14 1.2 HYDROLASE, GUANYLORIBONUCLEASE
1RGF 1996-10-14 1.2 HYDROLASE, GUANYLORIBONUCLEASE
4J5K 2014-05-28 1.23 Crystal structure analysis of Streptomyces aureofaciens ribonuclease Sa Y51F mutant
1I8V 2001-09-19 1.25 CRYSTAL STRUCTURE OF RNASE SA Y80F MUTANT
4J5G 2014-05-28 1.31 Crystal structure analysis of Streptomyces aureofaciens ribonuclease Sa T95A mutant
1BOX 1999-12-29 1.6 N39S MUTANT OF RNASE SA FROM STREPTOMYCES AUREOFACIENS
3A5E 2010-08-04 1.6 Crystal structure of 5K RNase Sa
1GMP 1993-10-31 1.7 COMPLEX OF RIBONUCLEASE FROM STREPTOMYCES AUREOFACIENS WITH 2'-GMP AT 1.7 ANGSTROMS RESOLUTION
1AY7 1999-03-02 1.7 RIBONUCLEASE SA COMPLEX WITH BARSTAR
1I70 2001-09-19 1.7 CRYSTAL STRUCTURE OF RNASE SA Y86F MUTANT
1GMR 1993-10-31 1.77 COMPLEX OF RIBONUCLEASE FROM STREPTOMYCES AUREOFACIENS WITH 2'-GMP AT 1.7 ANGSTROMS RESOLUTION
1UCI 2003-09-09 1.8 Mutants of RNase Sa
1UCK 2003-09-09 1.8 Mutants of RNase Sa
2SAR 1992-04-15 1.8 DETERMINATION AND RESTRAINED LEAST-SQUARES REFINEMENT OF THE CRYSTAL STRUCTURES OF RIBONUCLEASE SA AND ITS COMPLEX WITH 3'-GUANYLIC ACID AT 1.8 ANGSTROMS RESOLUTION
1SAR 1992-04-15 1.8 DETERMINATION AND RESTRAINED LEAST-SQUARES REFINEMENT OF THE CRYSTAL STRUCTURES OF RIBONUCLEASE SA AND ITS COMPLEX WITH 3'-GUANYLIC ACID AT 1.8 ANGSTROMS RESOLUTION
1GMQ 1993-10-31 1.8 COMPLEX OF RIBONUCLEASE FROM STREPTOMYCES AUREOFACIENS WITH 2'-GMP AT 1.7 ANGSTROMS RESOLUTION
1UCJ 2003-09-09 1.81 Mutants of RNase Sa
1UCL 2003-09-09 1.82 Mutants of RNase Sa
1RSN 1995-12-07 2.0 RIBONUCLEASE (RNASE SA) (E.C.3.1.4.8) COMPLEXED WITH EXO-2',3'-CYCLOPHOSPHOROTHIOATE

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Guanyl-specific ribonuclease Sa P05798 RNSA_KITAU