High Incidence of Disorder-Promoting Amino Acids in the Amino Terminus of Mature Proteins in Bacillus subtilis

Problem statement: Exported polypeptides are usually synthesized as preproteins which are composed with mature domains and the signal peptides. The foreign proteins are usually inefficiently secreted by the aid of signal peptides. Although we know that the mature protein played an important role in the protein export process, we do not know what properties of the mature domains are critical for protein export? This study explores the influence of the property of the mature domains on protein export in Bacillus subtilis. Approach: We analyzed the amino acid composition of 241 predicted exported proteins and 457 cytoplasmic proteins of Bacillus subtilis that have been previously reviewed using the program DAMBE, Codeprotein and Codeprotein Win. Results: Disorder-promoting amino acids in the first 14 residues of the mature domains were overrepresented in comparison to the residues in the NH₂-terminal region of cytoplasmic proteins or the cytoplasmic proteins. Further, the NH₂ terminus of the mature domain had more negatively charged residues and fewer positively charged residues than the NH2 terminus of the signal peptide. Conclusion/Recommendations: The presence of disordered domains in the NH₂-terminal regions of mature domains may provide the binding site and maintain the exported proteins in a secretion-competent conformation and the contrary charged residues distribution in the two ends of hydrophobic core may help form the hairpin-like structure of the signal peptide. These findings may have important implications for the understanding of the contribution of mature domains to membrane targeting and to translocation.