Signal Peptide Amino Acid Sequences in Escherichia Coli Contain Information Related to Final Protein Localization. A Multivariate Data Analysis

With few exceptions, the signal peptides from proteins inserted into, or translocated through, the membranes of gram-negative bacteria or the endoplasmic reticulum of eukaryotes have no sequence homologies. Therefore these signal peptides have not been considered to contain information related to the different final localizations of the proteins. In this study, 43 signal peptide amino acid sequences from proteins with different final localizations in Escherichia coli have been subjected to a multivariate data analysis. Each amino acid residue was characterized by 20 physico-chemical properties, yielding a multivariate property profile for each peptide. The similarities/dissimilarities in the property profiles for the signal peptides from different classes were compared with each other by generating few-dimensional partial least squares (PLS) discriminant plots. With this approach, signal peptides from proteins localized to the periplasmic space (PS), the outer membrane (OM), and the extracellular surroundings (excreted proteins), were separated into distinct groups. Signal peptides from pili proteins were not separated from the OM signal peptides and only partly from the PS signal peptides, but were clearly different from the signal peptides of the excreted proteins. Signal peptides from inner membrane proteins were similar to those of the PS peptides. The size and the hydrophobicity of different peptide segments were responsible for the separation of the signal peptide classes. For example, the hydrophobicity of the N-terminal segment of the signal peptides increased with an increased distance from the cytoplasm of the final localization for the corresponding proteins. Thus, many signal peptides from proteins with different final localizations in E. coli have different discernible physico-chemical profiles.