PROK2 and obesity due to melanocortin 4 receptor deficiency: In fact, knocking out PKR1 (Szatkowski et al., 2013) or MRAP2 (Asai et al., 2013) in mice causes obesity, and central administration of the PKR1 agonist PK2 leads to a significant decrease in food intake (Gardiner et al., 2010; Beale et al., 2013) and Figures 6 and 7.