PYY and obesity due to melanocortin 4 receptor deficiency: Recent studies have reported that the probiotic commensal bacteria strain Hafnia alvei (H. alvei), which produces the satietogenic peptide Casein-Like Protease B (ClpB), which mimics the effect of α-MSH, a key anorexigenic peptide involved in the regulation of appetite that stimulates in turn the release of PYY, reduces weight gain and adiposity in mouse models of obesity.