PLXNB1 and osteoporosis: In this study, Matsunaga and co-workers identified a high affinity (KD = 3.5 nM) thioether-closed cyclic peptide ligand to Plexin B1 (termed PB1m6), which was also a potent inhibitor of the interaction of Plexin B1 with Semaphorin 4D; an interaction that regulates osteoblast differentiation and is a possible target for osteoporosis [16].