Mycobacterial outer membrane porin PPE51 of 380 aas and about 8 TMSs. It is associated with the PE19 protein of 99 aas.  The complex probably transports a large range of nutrients and other solutes including propionamide, glucose and glycerol (Wang et al. 2020). PPE51 modulates membrane integrity in Mycobacterium marinum (Charitou et al. 2025).  The impermeable outer membrane of pathogenic mycobacteria presents a major obstacle to nutrient acquisition and antibiotic penetration. PPE51, a substrate of the ESX-5 secretion system, has previously been linked to glucose and glycerol uptake. Our study in Mycobacterium marinum reveals an unexpected additional role for PPE51 in maintaining membrane integrity. Loss of PPE51 not only impairs nutrient uptake but also causes increased membrane permeability, altered antibiotic susceptibility, and reduced virulence (Charitou et al. 2025).