PDBsum entry 1bns

Endonuclease

PDB id: 1bns

Contents

Protein chains

108 a.a. *

Waters ×224

* Residue conservation analysis

PDB id:

1bns

Name:

Endonuclease

Title:

Structural studies of barnase mutants

Structure:

Barnase. Chain: a, b, c. Engineered: yes

Source:

Bacillus amyloliquefaciens. Organism_taxid: 1390

Resolution:

2.05Å R-factor: 0.169

Authors:

Y.W.Chen

Key ref:

Y.W.Chen et al. (1993). Contribution of buried hydrogen bonds to protein stability. The crystal structures of two barnase mutants. J Mol Biol, 234, 1158-1170. PubMed id: 8263918

Date:

11-Apr-94 Release date: 22-Jun-94

Protein chains

P00648  (RNBR_BACAM) -  Ribonuclease from Bacillus amyloliquefaciens

Seq: 157 a.a.

Struc: 108 a.a.*

* PDB and UniProt seqs differ at 1 residue position (black cross)

Enzyme reactions

• Enzyme class: E.C.3.1.27.- - ?????

J Mol Biol 234:1158-1170 (1993)

PubMed id: 8263918

Contribution of buried hydrogen bonds to protein stability. The crystal structures of two barnase mutants.

Y.W.Chen, A.R.Fersht, K.Henrick.

ABSTRACT

The crystal structures of two barnase mutants, Tyr78-->Phe and Ser91-->Ala, have been determined to 2.2 A resolution. In both cases, a buried hydroxyl group that makes two hydrogen bonds within the protein was replaced by a hydrogen atom. It is found that neither mutation causes any structural changes, within the limits of error, compared with wild-type and so are confirmed to be non-disruptive. Solvent molecules are not observed in the cavities created by removal of the respective hydroxyl groups and no new interactions are introduced. The local water structure surrounding both sites of mutation is well conserved and resembles that of the wild-type. All four water molecules making contacts with the side-chain of residue 78 and two water molecules nearest to residue 91 in the wild-type are found within a sphere of 0.5 A radius, at the equivalent positions of the respective mutant. No new water molecules are found bound to any of the hydrogen bond donor or acceptor residues involved in these two mutation sites. Previous protein engineering experiments established that the solvent-inaccessible phenolic OH of Tyr78 that makes hydrogen bonds with two uncharged groups (main-chain NH and CO) contributes 1.4 kcal mol-1 to protein stability, while the solvent-inaccessible OH of Ser91 that makes hydrogen bonds with an uncharged main-chain NH and a charged group (O gamma 1) contributes 1.9 kcal mol-1. These stability measurements can now be attributed primarily to the loss of the hydrogen bonding interactions because both mutations neither disrupt the respective protein and local solvent structures, upset the overall hydrogen bonding pattern nor introduce new interactions. The mutations Tyr78-->Phe and Ser91-->Ala are thus good examples of "non-disruptive deletions" and the results of mutagenesis can be analysed at the simplest level.