1L65

TOLERANCE OF T4 LYSOZYME TO MULTIPLE XAA (RIGHT ARROW) ALA SUBSTITUTIONS: A POLYALANINE ALPHA-HELIX CONTAINING TEN CONSECUTIVE ALANINES

Summary for 1L65

• Entry DOI: 10.2210/pdb1l65/pdb
• Descriptor: LYSOZYME, CHLORIDE ION, BETA-MERCAPTOETHANOL, ... (4 entities in total)
• Functional Keywords: hydrolase (o-glycosyl)
• Biological source: Enterobacteria phage T4
• Total number of polymer chains: 1
• Total formula weight: 18811.52

Authors

Heinz, D.,Matthews, B.W. (deposition date: 1991-09-23, release date: 1991-10-15, Last modification date: 2024-02-14)

Primary citation

Heinz, D.W.,Baase, W.A.,Matthews, B.W.
Folding and function of a T4 lysozyme containing 10 consecutive alanines illustrate the redundancy of information in an amino acid sequence.
Proc.Natl.Acad.Sci.USA, 89:3751-3755, 1992

PubMed Abstract: Single and multiple Xaa----Ala substitutions were constructed in the alpha-helix comprising residues 39-50 in bacteriophage T4 lysozyme. The variant with alanines at 10 consecutive positions (A40-49) folds normally and has activity essentially the same as wild type, although it is less stable. The crystal structure of this polyalanine mutant displays no significant change in the main-chain atoms of the helix when compared with the wild-type structure. The individual substitutions of the solvent-exposed residues Asn-40, Ser-44, and Glu-45 with alanine tend to increase the thermostability of the protein, whereas replacements of the buried or partially buried residues Lys-43 and Leu-46 are destabilizing. The melting temperature of the lysozyme in which Lys-43 and Leu-46 are retained and positions 40, 44, 45, 47, and 48 are substituted with alanine (i.e., A40-42/44-45/47-49) is increased by 3.1 degrees C relative to wild type at pH 3.0, but reduced by 1.6 degrees C at pH 6.7. In the case of the charged amino acids Glu-45 and Lys-48, the changes in melting temperature indicate that the putative salt bridge between these two residues contributes essentially nothing to the stability of the protein. The results clearly demonstrate that there is considerable redundancy in the sequence information in the polypeptide chain; not every amino acid is essential for folding. Also, further evidence is provided that the replacement of fully solvent-exposed residues within alpha-helices with alanines may be a general way to increase protein stability. The general approach may permit a simplification of the protein folding problem by retaining only amino acids proven to be essential for folding and replacing the remainder with alanine.

PubMed: 1570293
DOI: 10.1073/pnas.89.9.3751

Experimental method

X-RAY DIFFRACTION (1.7 Å)