Objectives: The purpose of this study was to characterize Tf S-layer biochemically and genetically.
Methods: The S-layer from Tf 43037 were isolated, purified, and analyzed by amino acid sequencing and MALDI-TOF mass spectrometry. The S-layer genes were identified in silico from the unfinished Tf genome sequences, based on the partial amino acid sequences of the S-layer glycoproteins, cloned by PCR, and their sequences were determined.
Results: It was determined that the S-layer consisted of the 200- and 210-kD glycoproteins. These are two different proteins encoded by separate genes, tfsA and tfsB. The tfsA (3.5 kb) and tfsB (4.1 kb) genes encode for 135- and 152-kD proteins, respectively. An apparent discrepancy (135- vs. 200-kD and 152- vs. 210-kD) in molecular weights is accounted for carbohydrate residues attached to the core proteins. Further analysis showed that TfsA and TfsB possess putative signal peptide sequences; however, these exhibited no homology to other known S-layer proteins.
Conclusion: The S-layer of Tf consists of two large glycoproteins encoded by separate genes, and it has a unique structure showing no homology to other S-layers of prokaryotic organisms.