This is the C-terminal helix from COP9 signalosome complex subunit 1, an essential component of the COP9 signalosome complex (CSN), which involved in various cellular and developmental processes [1,2].

1: Crystal structure of the human COP9 signalosome. Lingaraju GM, Bunker RD, Cavadini S, Hess D, Hassiepen U, Renatus M, Fischer ES, Thoma NH; Nature. 2014;512:161-165. PMID:25043011

2: Structural basis of Cullin 2 RING E3 ligase regulation by the COP9 signalosome. Faull SV, Lau AMC, Martens C, Ahdash Z, Hansen K, Yebenes H, Schmidt C, Beuron F, Cronin NB, Morris EP, Politis A; Nat Commun. 2019;10:3814. PMID:31444342