MbtH-like proteins (MLPs) are small, bacterial proteins that are nearly alwaysencoded within a nonribosomal peptide biosynthetic gene cluster. MLPs are essential for solubility and/or activity of the nonribosomal peptide synthetases encoded in these gene clusters. MbtH, which gives the name to this family, is the eighth gene in the mycobactin biosynthesis gene cluster in Mycobacterium tuberculosis.