Schistosoma mansoni fatty acid binding protein: specificity and functional control as revealed by crystallographic structure.
Schistosoma mansoni fatty acid binding protein (Sm14) was crystallized with bound oleic acid (OLA) and arachidonic acid (ACD), and their structures were solved at 1.85 and 2.4 A resolution, respectively. Sm14 is a vaccine target for schistosomiasis, the second most prevalent parasitic disease in humans. The parasite is unable to synthesize fatty acids depending on the host for these nutrients. Moreover, arachidonic acid (ACD) is required to synthesize prostaglandins employed by schistosomes to evade the host's immune defenses. In the complex, the hydrocarbon tail of bound OLA assumes two conformations, whereas ACD adopts a unique hairpin-looped structure. ACD establishes more specific interactions with the protein, among which the most important is a pi-cation bond between Arg78 and the double bond at C8. Comparison with homologous fatty acid binding proteins suggests that the binding site of Sm14 is optimized to fit ACD. To test the functional implications of our structural data, the affinity of Sm14 for 1,8-anilinonaphthalenesulfonic acid (ANS) has been measured; moreover the binding constants of six different fatty acids were determined from their ability to displace ANS. OLA and ACD exhibited the highest affinities. To determine the rates of fatty acid binding and dissociation we carried out stopped flow kinetic experiments monitoring displacement by (and of) ANS. The binding rate constant of ligands is controlled by a slow pH dependent conformational change, which we propose to have physiological relevance.
Department of Biochemical Sciences A. Rossi Fanelli, CNR Institute of Molecular Biology and Pathology and Istituto Pasteur-Fondazione Cenci Bolognetti, University of Rome La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy.
Francesco
F
Angelucci
Kenneth A
KA
Johnson
Paola
P
Baiocco
Adriana E
AE
Miele
Maurizio
M
Brunori
Cristiana
C
Valle
Fabio
F
Vigorosi
Anna Rita
AR
Troiani
Piero
P
Liberti
Donato
D
Cioli
Mo-Quen
MQ
Klinkert
Andrea
A
Bellelli
D000818:Animals; D016718:Arachidonic Acid / Q000737:chemistry / Q000378:metabolism; D002352:Carrier Proteins / Q000008:administration & dosage / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000008:administration & dosage / Q000737:chemistry / Q000276:immunology; D050556:Fatty Acid-Binding Proteins; D015801:Helminth Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D007700:Kinetics; D008024:Ligands; D046911:Macromolecular Substances; D051379:Mice; D019301:Oleic Acid / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D012550:Schistosoma mansoni / Q000737:chemistry*; D013045:Species Specificity; D022223:Vaccines, Subunit / Q000008:administration & dosage / Q000276:immunology
D002352:Carrier Proteins; D000939:Epitopes; D050556:Fatty Acid-Binding Proteins; D015801:Helminth Proteins; D008024:Ligands; D046911:Macromolecular Substances; D022223:Vaccines, Subunit; D016718:Arachidonic Acid; D019301:Oleic Acid