The electronic structure of S-layer proteins from Lactobacillus brevis

The valence electronic structure of the S-layer of Lactobacillus brevis is determined using synchrotron-based photoelectron spectroscopy and soft X-ray absorption spectroscopy. Spectra are compared to experimental work on amino-acids and S-layers of Bacillus sphaericus. While it is indeed possible to identify energy levels with those of natural amino-acids, distinct energy shifts are indeed observed which cannot be reconciled using such simple comparisons. Furthermore a strong nitrogen signal observed in both the occupied and unoccupied energy levels suggests that the Lactobacillus brevis protein is amine-terminated. A discussion of the surface of this protein is given.