SKP1 and obesity due to melanocortin 4 receptor deficiency: Moreover, CUL1 (along with SKP1 (S-phase-kinase-associated protein 1) and F-Box protein) forms the largest E3 ubiquitin ligase family (Skp1-Cullin1-F-box (SCF)) E3 ligase is known for controlling obesity with an association of Skp2 [58].