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1.  Structural and functional analysis of betaine aldehyde dehydrogenase from Staphylococcus aureus  
The purified putative betaine aldehyde dehydrogenase SACOL2628 from the early methicillin-resistant S. aureus COL has betaine aldehyde dehydrogenase activity and is structurally similar to aldehyde dehydrogenases.
When exposed to high osmolarity, methicillin-resistant Staphylococcus aureus (MRSA) restores its growth and establishes a new steady state by accumulating the osmoprotectant metabolite betaine. Effective osmoregulation has also been implicated in the acquirement of a profound antibiotic resistance by MRSA. Betaine can be obtained from the bacterial habitat or produced intracellularly from choline via the toxic betaine aldehyde (BA) employing the choline dehydrogenase and betaine aldehyde dehydrogenase (BADH) enzymes. Here, it is shown that the putative betaine aldehyde dehydrogenase SACOL2628 from the early MRSA isolate COL (SaBADH) utilizes betaine aldehyde as the primary substrate and nicotinamide adenine dinucleotide (NAD+) as the cofactor. Surface plasmon resonance experiments revealed that the affinity of NAD+, NADH and BA for SaBADH is affected by temperature, pH and buffer composition. Five crystal structures of the wild type and three structures of the Gly234Ser mutant of SaBADH in the apo and holo forms provide details of the molecular mechanisms of activity and substrate specificity/inhibition of this enzyme.
PMCID: PMC4427200  PMID: 25945581
betaine aldehyde dehydrogenase; Staphylococcus aureus; structural genomics; high-throughput approach; infectious diseases
2.  Characterization of Fibrinogen Binding by Glycoproteins Srr1 and Srr2 of Streptococcus agalactiae* 
The Journal of Biological Chemistry  2013;288(50):35982-35996.
Background: The serine-rich repeat glycoproteins Srr1 and Srr2 are surface adhesins of Streptococcus agalactiae important for pathogenicity.
Results: Both Srrs bind tandem repeats of the fibrinogen Aα chain, but Srr2 has greater affinity explained by structure-function analysis of the Srrs.
Conclusion: A dock, lock, and latch mechanism describes the Srr-fibrinogen interaction.
Significance: The higher affinity of Srr2 may contribute to the hypervirulence of Srr2-expressing strains.
The serine-rich repeat glycoproteins of Gram-positive bacteria comprise a large family of cell wall proteins. Streptococcus agalactiae (group B streptococcus, GBS) expresses either Srr1 or Srr2 on its surface, depending on the strain. Srr1 has recently been shown to bind fibrinogen, and this interaction contributes to the pathogenesis of GBS meningitis. Although strains expressing Srr2 appear to be hypervirulent, no ligand for this adhesin has been described. We now demonstrate that Srr2 also binds human fibrinogen and that this interaction promotes GBS attachment to endothelial cells. Recombinant Srr1 and Srr2 bound fibrinogen in vitro, with affinities of KD = 2.1 × 10−5 and 3.7 × 10−6 m, respectively, as measured by surface plasmon resonance spectroscopy. The binding site for Srr1 and Srr2 was localized to tandem repeats 6–8 of the fibrinogen Aα chain. The structures of both the Srr1 and Srr2 binding regions were determined and, in combination with mutagenesis studies, suggest that both Srr1 and Srr2 interact with a segment of these repeats via a “dock, lock, and latch” mechanism. Moreover, properties of the latch region may account for the increased affinity between Srr2 and fibrinogen. Together, these studies identify how greater affinity of Srr2 for fibrinogen may contribute to the increased virulence associated with Srr2-expressing strains.
PMCID: PMC3861647  PMID: 24165132
Bacterial Adhesion; Bacterial Pathogenesis; Fibrinogen; Protein Crystallization; Streptococcus; Streptococcus agalactiae; Prot
3.  Structural characterization and comparison of three acyl-carrier-protein synthases from pathogenic bacteria 
The structural characterization of acyl-carrier-protein synthase (AcpS) from three different pathogenic microorganisms is reported. One interesting finding of the present work is a crystal artifact related to the activity of the enzyme, which fortuitously represents an opportunity for a strategy to design a potential inhibitor of a pathogenic AcpS.
Some bacterial type II fatty-acid synthesis (FAS II) enzymes have been shown to be important candidates for drug discovery. The scientific and medical quest for new FAS II protein targets continues to stimulate research in this field. One of the possible additional candidates is the acyl-carrier-protein synthase (AcpS) enzyme. Its holo form post-translationally modifies the apo form of an acyl carrier protein (ACP), which assures the constant delivery of thioester intermediates to the discrete enzymes of FAS II. At the Center for Structural Genomics of Infectious Diseases (CSGID), AcpSs from Staphylococcus aureus (AcpSSA), Vibrio cholerae (AcpSVC) and Bacillus anthracis (AcpSBA) have been structurally characterized in their apo, holo and product-bound forms, respectively. The structure of AcpSBA is emphasized because of the two 3′,5′-adenosine diphosphate (3′,5′-ADP) product molecules that are found in each of the three coenzyme A (CoA) binding sites of the trimeric protein. One 3′,5′-ADP is bound as the 3′,5′-ADP part of CoA in the known structures of the CoA–AcpS and 3′,5′-ADP–AcpS binary complexes. The position of the second 3′,5′-ADP has never been described before. It is in close proximity to the first 3′,5′-­ADP and the ACP-binding site. The coordination of two ADPs in AcpSBA may possibly be exploited for the design of AcpS inhibitors that can block binding of both CoA and ACP.
PMCID: PMC3447402  PMID: 22993090
acyl-carrier-protein synthase; acyl carrier protein; type II fatty-acid synthesis; inhibition; 3′,5′-adenosine diphosphate; coenzyme A

Results 1-3 (3)