Univ Sci & Technol China, Natl Lab Phys Sci Microscale, Hefei 230026, Anhui, Peoples R China
; Univ Sci & Technol China, Sch Life Sci, Hefei 230026, Anhui, Peoples R China
; Chinese Acad Sci, Beijing Synchrotron Radiat Facil, Inst High Energy Phys, Beijing 100039, Peoples R China
Kti11p is a small, highly conserved CSL zinc finger-containing protein found in many eukaryotes. It was first identified as one of the factors required for maintaining the sensitivity of Saccharomyces cerevisiae to Kluyveromyces lactis zymocin. Then, it was found to be identical to Dph3, a protein required for diphthamide biosynthesis on eEF-2, the target of diphtheria toxin and Pseudomonas exotoxin A, in both yeast and higher eukaryotes. Furthermore, Kti11p/Dph3 was found to physically interact with core-Elongator, ribosomal proteins, eEF-2, two other proteins required for diphthamide modification on eEF-2, and De1GEF. Here, we determined the solution structure of Kti11p using NMR, providing the first structure of the CSL-class zinc-binding protein family. We present the first experimental evidence that Kti11p can bind a single Zn2+ ion by its four conserved cysteine residues. The major structure of Kti11p comprises a beta sandwich as well as an a helix. Moreover, a structure-based similarity search suggests that it represents a novel structure and may define a new family of the zinc ribbon fold group. Therefore, our work provides a molecular basis for further understanding the multiple functions of Kti11p/Dph3 in different biological processes.