Longin-Like Folds. Longin domain interaction with small GTPase and spatial DUF254/CHiPS domain conservations. DUF254 and CHiPS family conservations were mapped to a representative longin domain structure (1nrj) based on the alignment. Conservations are represented with a rainbow color ramp from blue for less conserved positions to red for mainly conserved positions, and the N termini and C termini are labeled accordingly. (A) Interaction of the Srx longin domain (rainbow) with the GTP (red bonds) bound state of the signal recognition particle receptor subunit small GTPase (gray) is mediated by conserved longin domain residues positioned near the GTPase switch loops (colored black). Core longin domain secondary structural elements are labeled according to topology. DUF254 longin domain conservations (B), and CHiPS family longin domain conservations (C) mapped to the srx structure (1nrjA) show a similar spatial arrangement of conserved positions.