123rd General Meeting of the KCS

Type Poster Presentation
Area Life Chemistry
Room No. Exhibition Hall 2
Time 4월 19일 (금요일) 11:00~12:30
Code LIFE.P-381
Subject Structural insights into catalytic mechanisms of the two major beta-carbonic anhydrases from the fungal pathogen Aspergillus fumigatus
Authors Subin Kim, Mi Sun Jin*
School of Life Sciences, Gwangju Institute of Science and Technology, Korea
Abstract In fungi, the beta-class of carbonic anhydrases (beta-CAs) are ubiquitous zinc metalloenzymes that are essential for their growth, survival, differentiation, and virulence. Here we report the crystal structures and biochemical characterization of two tetrameric beta-CAs, CafA and CafB, from Aspergillus fumigatus, known as the major cause of invasive aspergillosis. Both enzymes exhibit apparent in vitro CO2 hydration activity. Despite the overall similarities in structures, there are notable differences in the catalytic active sites. In CafA, the zinc ion is tetrahedrally coordinated by the three conserved residues (C119, H175, and C178) and a hydrated carbon dioxide (bicarbonate), indicating that it has “open” conformation (Type-I class). In contrast, CafB shows novel active site in which the disulfide bond formation between zinc-ligating two cysteines (C57 and C116) expels the zinc ion, and closes the active site incapable of binding a substrate. Site-directed mutagenesis represents a potential role of Y159 as a proton-coupled electron transfer during oxidative inactivation. CafB also has a non-catalytic (inhibitory) site for bicarbonate binding to regulate its activity allosterically. Our results suggest that the two closely related CafA and CafB utilize the different types of catalytic mechanisms; CafA is active in a broad range of pH, but CafB is subject to oxidative inactivation and/or allosteric substrate inhibition. A. fumigatus may use this sophisticated activity-withholding strategy to enhance survival capacity in the infected human.
E-mail ksb1201@gist.ac.kr