View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Structure 14, 1251–1261, August 2006 ª2006 Elsevier Ltd All rights reserved DOI 10.1016/j.str.2006.06.008 Prokaryotic Type II and Type III Pantothenate Kinases: The Same Monomer Fold Creates Dimers with Distinct Catalytic Properties Bum Soo Hong,1,6 Mi Kyung Yun,3,6 Yong-Mei Zhang,4 from their bacterial counterparts (Calder et al., 1999), Shigeru Chohnan,4,7 Charles O. Rock,4,5 and they are feedback inhibited by CoA or its thioesters Stephen W. White,3,5 Suzanne Jackowski,4,5 to achieve a tight and tissue-specific regulation of the Hee-Won Park,1,2 and Roberta Leonardi4,* cofactor level (Rock et al., 2000, 2002; Zhang et al., 1 Structural Genomics Consortium 2005). 2 Department of Pharmacology Bacteria possess three types of pantothenate kinases University of Toronto (CoaAs) that differ in sequence, regulation, substrate af- Toronto, Ontario M5G 1L5 finity, and specificity (Brand and Strauss, 2005; Leonardi Canada et al., 2005a; Vallari et al., 1987). The type I CoaA is 3 Department of Structural Biology widely distributed, and the prototypical member is the 4 Department of Infectious Diseases Escherichia coli CoaA (EcCoaA), which is encoded by St. Jude Children’s Research Hospital the coaA gene (Song and Jackowski, 1992, 1994) and Memphis, Tennessee 38105 is regulated through feedback inhibition by CoA and 5 Department of Molecular Sciences CoA thioesters (Vallari et al., 1987). EcCoaA is a dimer University of Tennessee Health Science Center of identical subunits and is structurally classified as Memphis, Tennessee 38163 a P loop kinase containing a Walker A motif (Ivey et al., 2004; Yun et al., 2000). The pantothenate kinase from Staphylococcus aureus (SaCoaA) is the prototypical Summary type II enzyme, and it is refractory to feedback inhibition by CoA or its thioesters (Leonardi et al., 2005a). This lack Three distinct isoforms of pantothenate kinase (CoaA) of regulation allows the accumulation of millimolar con- in bacteria catalyze the first step in coenzyme A bio- centrations of CoA, which is the major intracellular thiol synthesis. The structures of the type II (Staphylococ- in this organism (delCardayre et al., 1998). There is par- cus aureus, SaCoaA) and type III (Pseudomonas aeru- ticular interest in the type II SaCoaA protein because it is ginosa, PaCoaA) enzymes reveal that they assemble related to the four eukaryotic isoforms of pantothenate nearly identical subunits with actin-like folds into di- kinase, PanK1a, PanK1b, PanK2, and PanK3 (Cheek mers that exhibit distinct biochemical properties. et al., 2005). Alignment of the human PanK2 and SaCoaA PaCoaA has a fully enclosed pantothenate binding sequences (Figure 1A) reveals that the region of greatest pocket and requires a monovalent cation to weakly similarity corresponds to the conserved phosphate bind ATP in an open cavity that does not interact binding P loop DxGG(T,S)T(S,G)xxK(R,C) motif charac- with the adenine nucleotide. Pantothenate binds to teristic of members of the acetate and sugar kinases/ an open pocket in SaCoaA that strongly binds ATP Hsc70/actin (ASKHA) family (Bork et al., 1992; Kabsch by using a classical P loop architecture coupled with and Holmes, 1995). Finally, a number of bacteria, includ- specific interactions with the adenine moiety. The Pa- ing pathogens such as Helicobacter pylori and Pseudo- CoaAPan binary complex explains the resistance of monas aeruginosa, possess a type III enzyme. The type bacteria possessing this isoform to the pantothena- III CoaA from H. pylori, HpCoaA, is not regulated by mide antibiotics, and the similarity between SaCoaA CoA or its thioesters, and, unlike the type I and II CoaAs and human pantothenate kinase 2 explains the molec- that have similar Kms for the substrates in the micro- ular basis for the development of the neurodegenera- molar range (Leonardi et al., 2005a; Song and Jacko- tive phenotype in three mutations in the human wski, 1994), it exhibits an unusually high Km for ATP protein. (w10 mM) (Brand and Strauss, 2005). The absence of any obvious sequence similarity be- tween the three types of bacterial CoaAs, and their strik- Introduction ingly different biochemical properties, prompted us to investigate the structural basis of this diversity. Our Coenzyme A (CoA) is an indispensable cofactor in all bi- study reports the crystal structures of the type II ological systems, where it functions as the major acyl SaCoaAAMP-PNP complex, the type III PaCoaA apo- group carrier (Leonardi et al., 2005b). The universal enzyme, and the PaCoaAPan complex. Both enzymes CoA biosynthetic pathway consists of five enzymatic share the same actin-like monomer fold, but they asso- steps, the first of which is the phosphorylation of panto- ciate to form two very different dimeric architectures. thenate (Pan), or vitamin B5, catalyzed by pantothenate Furthermore, by combining the structural information kinase. Pantothenate kinase is the key regulatory step in on how SaCoaA and PaCoaA bind the phosphoryl donor CoA biosynthesis (Leonardi et al., 2005b). The eukary- and Pan, respectively, we can assemble an accurate otic pantothenate kinase isoforms (PanKs) are distinct picture of the catalytic ternary complex for each en- zyme. These models provide a structural framework for understanding the substrate specificities of each en- *Correspondence: [email protected] zyme and their distinct catalytic mechanisms. Both the 6 These authors contributed equally to this work. 7 Present address: Department of Bioresource Science, College of type I and type II CoaAs recognize the pantothenamide Agriculture, Ibaraki University, 3-21-1 Chu-ou, Ami, Ibaraki class of antimetabolites (Leonardi et al., 2005a; Strauss 300-0393, Japan. and Begley, 2002), whereas the type III CoaAs do not Structure 1252 see the Supplemental Data available with this article on- line). The monomer structures are very similar and com- prise two a/b domains, and each domain contains a mixed five-stranded b sheet surrounded by a helices (Figures 2A and 2C). Domain I consists of strands b1– b5 in the order 3-2-1-4-5 with strand b2 antiparallel to the others, and helices a1, a2, a3, and a8. Domain II con- tains strands b6–b10 in the order 8-7-6-9-10 with strand b7 antiparallel to the others, and helices a3, a4, a5, a6, a7, and a8. The folding topologies of each domain are identical and place them in the actin superfamily. They are tightly associated such that helices a3 and a8 are common to each domain at the domain interface, with the C-terminal a8 completing the domain I substructure. A structural similarity search of the protein database with the VAST program revealed that the fold of SaCoaA and PaCoaA places them in the ASKHA superfamily (Bork et al., 1992; Cheek et al., 2002; Kabsch and Holmes, 1995). Members of this family have the same relative orientations of domains I and II. The classic P loops in the kinase fold are between the first and second b strands of each domain (strands b1 and b2 of domain I and strands b6 and b7 of domain II), and these meet at the center of the domain interface. The domain I P loop has the classical signature sequence, whereas do- main II can be considered a ‘‘pseudo kinase’’ domain. Domain II is larger than domain I by virtue of two addi- tional helices, a4 and a5, and an extended a6 compared to its counterpart, a1(Figures 2A and 2C). Both proteins crystallized as a dimer in the asymmet- Figure 1. Alignment of Type II and Type III CoaAs ric unit, and the monomers of this dimer are related by (A) Alignment of the primary sequences of SaCoaA and human a noncrystallographic 2-fold rotation axis. The dimen- PanK2. Residues highlighted in red were investigated by site-di- sions of the dimers are consistent with the hydrody- rected mutagenesis, and those indicated with an asterisk (*) are con- namic data on the two soluble proteins (Figure S1)(Leo- served between SaCoaA and human PanK2 and are mutated in nardi et al., 2005a). Although the SaCoaA and PaCoaA PKAN patients. The residues in the dimer interface conserved be- tween the two proteins are indicated with a ‘‘+.’’ monomers have very similar structures, they each con- (B) Alignment of the primary sequences of the type III CoaAs from tain a loop region that is absent from the other enzyme, P. aeruginosa (NCBI gij15599475), B. subtilis (NCBI gij16077138, which results in their assembly into dimers with dis- corrected in GenBank acc. #AY912104), and H. pylori (NCBI tinctly different architectures (Figures 2B and 2D). Sa- gij15645481). Sequence identities are: PaCoaA/BsCoaA = 19%, CoaA contains a loop between helices a4 and a5 that PaCoaA/HpCoaA = 21%, HpCoaA/BsCoaA = 14%, and PaCoaA/ packs against a6(Figure 2B). Conversely, PaCoaA has SaCoaA = 12%. The residues in the dimer interface conserved in b a at least two of the three sequences are indicated with a ‘‘+.’’ a loop inserted between 5 and 3 that contains a short b ribbon that associates with the outside b8 strand of the domain II b sheet (Figure 2D). Although both loops con- accept these compounds as substrates (Brand and tribute to the monomer-monomer interface, they do so Strauss, 2005). The different dimeric structures of in different ways. The SaCoaA loop mainly interacts SaCoaA and PaCoaA explain the resistance of P. aerugi- with a40, whereas the PaCoaA loop interacts with the nosa to the pantothenamide class of drugs. Finally, the a50–a60 loop (the prime sign indicates an element in the structure of the SaCoaAAMP-PNP binary complex pro- other monomer). As a result, the long a6 helices within vides insights into the structure and catalytic mecha- the SaCoaA dimer interact extensively via a parallel nism of the mammalian pantothenate kinases.