Edited by Stuart Ferguson Keywords:Signal transduction Penicillin-binding protein and Ser/Thr protein kinase-associated domain Peptidoglycan b-Lactam antibiotics Protein structure Streptococcus pneumoniae a b s t r a c tThe eukaryotic-type serine/threonine kinase StkP from Streptococcus pneumoniae is an important signal-transduction element that regulates the expression of numerous pneumococcal genes. We have expressed the extracellular C-terminal domain of StkP kinase (C-StkP), elaborated a threedimensional structural model and performed a spectroscopical characterization of its structure and stability. Biophysical experiments show that C-StkP binds to synthetic samples of the cell wall peptidoglycan (PGN) and to b-lactam antibiotics, which mimic the terminal portions of the PGN stem peptide. This is the first experimental report on the recognition of a minimal PGN unit by a PASTAcontaining kinase, suggesting that non-crosslinked PGN may act as a signal for StkP function and pointing to this protein as an interesting target for b-lactam antibiotics.

Wheat germ agglutinin (WGA), a chitin binding lectin, has attracted increasing interest because of its unique characteristics such as conformational stability, binding specificity and transcytosis capacity. To pave the way for the study of the molecular basis of WGA's structural stability and binding capacity, as well as to facilitate its use in biomedical and biotechnological developments, we produced recombinant WGA and its 4 isolated hevein‐like domains in a bacterial system. All the proteins were expressed as fusion constructs linked to a thioredoxin domain, which was enzymatically or chemically released. The structural and ligand‐binding properties of recombinant WGA were similar to the wild lectin. The 4 isolated domains folded and were ligand‐binding competent, indicating that each domain constitutes an independent folding unity. The biophysical characterization of the recombinant domains sheds new light on the intricate folding and binding behavior of this emblematic lectin.

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