In Vivo and In Vitro Protein-Peptidoglycan Interactions

Bacteria have developed a number of trans-envelope systems to transport molecules or assemble organelles across bacterial envelopes. However, bacterial envelopes contain a rigid netlike peptidoglycan structure that protects cells from osmotic lysis. Trans-envelope systems thus must interact with the peptidoglycan barrier to generate gaps or anchor structures to the peptidoglycan scaffold. Here we describe methods to use in vivo cross-linking and in vitro co-sedimentation to study protein-peptidoglycan interactions in Gram-negative bacteria. In particular, we address important considerations to ensure the specificity of the interactions in question.