A transpeptidase that forms peptide cross-links between adjacent glycan strands in cell wall peptidoglycan (PG). Part of the elongasome machinery that synthesizes peripheral PG. Interacts with MreC in the elongasome. Localizes to the midcell division sites, colocalizes with StkP. Comparison of drug-sensitive and drug-resistant protein structures shows the active site is highly flexible. Essential, it cannot be deleted (PubMed:8454182). Cells depleted of PBP2b continue to grow more slowly than wild-type until at least 12 hours after expression stops. Cells form very long chains and have an altered shape, becoming lentil-like rather than ellipsoid. Cells are more sensitive to amidase and have an altered stem peptide composition (PubMed:23873916). Structures 2WAD and 2WAE are from strain 5204, a clinical, drug-resistant strain with 58 mutations in compared to strain R6. Belongs to the transpeptidase family. Extended N-terminus.