Carboxy terminal residues as predictors and regulators of protein stability
Compositions and methods are provided that are useful for predicting and controlling the stability of expressed polypeptides. The compositions and methods may be used to predict and as desired, increase or decrease the stability of proteins recombinantly expressed in mycobacteria, for example DesA3 expressed in Mycobacterium smegmatis . At the C terminus and the penultimate position, substitution to residues with charged side chains, large non-polar side chains, or no side chains can be used to reduce or inhibit the protein degradation. At the antepenultimate position from the C terminus, residues with no side chain or acidic side chains can increase the stability, i.e. reduce or inhibit the protein degradation. The combinational substitution of only the last three residues of polypeptides can make the polypeptides more stable during heterologous expression in mycobacterial hosts.
1. A method for increasing the stability of a polypeptide, wherein the last two amino acid residues of the carboxy terminal sequence of the polypeptide are independently selected from Ala, Cys, Ile, Leu, Ser, Thr, and Val, and wherein the antepenultimate amino acid residue of the carboxy terminal sequence of the polypeptide is not Asp, Gly, Glu or His, against degradation by a C-terminal specific mycobacterium protease, comprising the step of altering one or more of the last three amino acid residues at the carboxy terminus of the polypeptide,
wherein the alteration is selected from the group consisting of amino acid substitution, amino acid insertion, and amino acid deletion, and
wherein the alteration results in at least one of:
(a) one or both of the last two amino acid residues of the carboxy terminal sequence of the polypeptide being selected from the group consisting of Arg, Asp, Glu, Gly, His, Lys, Phe, Pro, Trp, and Tyr, and
(b) the antepenultimate residue of the carboxy terminal sequence of the polypeptide being selected from the group consisting of Asp, Gly, Glu, and His; and
measuring the stability of the altered polypeptide against degradation by the C-terminal specific mycobacterium protease,
whereby the stability of the altered polypeptide against degradation by the C-terminal specific mycobacterium protease is increased as compared to the unaltered polypeptide.
2. The method of claim 1 wherein the alteration results in the sequence Asp-Lys-Asp, Leu-Glu-Ala, Leu-Lys-Ala, or Leu-Ala-Asp for the last three amino acid residues at the carboxy terminus of the polypeptide.
3. The method of claim 1 , wherein the last three amino acid residues of the carboxy terminal sequence of the polypeptide before the polypeptide is altered are Leu-Ala-Ala.