Immobilization of proteins onto solid supports is important in the preparation of functional protein microarrays and in the development of bead-based bioassays, biosensors, and industrial biocatalysts. In order to generate the stable, functional, and homogeneous materials required for these applications, attention has focused on methods that enable the efficient and site-specific covalent immobilization of recombinant proteins onto a wide range of platforms. To this end, the phosphopantetheinyl transferase Sfp was employed to catalyze the direct immobilization of recombinant proteins bearing the small, genetically encoded ybbR tag onto surfaces functionalized with CoA. Using mass spectrometry, it was shown that the Sfp catalyzes immobilization of a model acyl carrier protein (ACP) onto CoA-derivatized PEGA resin beads through specific covalent bond formation. Luciferase (Luc) and glutathione-S-transferase (GST) ybbR-fusion proteins were similarly immobilized onto PEGA resin retaining high levels of enzyme activity. This strategy was also successfully applied for the immobilization of the ACP, as well as ybbR-Luc, -GST, and -thioredoxin fusion proteins, on hydrogel microarray slides. Overall, the Sfp-catalyzed surface ligation is mild, quantitative, and rapid, occurring in a single step without prior chemical modification of the target protein. Immobilization of the target proteins directly from a cell lysate mixture was also demonstrated.

Calcium-dependent antibiotics (CDA) are cyclic lipopeptides assembled by nonribosomal peptide synthetase (NRPS) enzymes. Active site modification of the 3-methyl glutamate activating adenylation (A) domain of the CDA NRPS enables the incorporation of synthetic 3-methyl glutamine into CDA. This provides the first example of how A-domains can be engineered to introduce synthetic "non-natural" amino acids into nonribosomal peptides.

Loading of the replicative ring helicase onto the origin of replication (oriC) is the final outcome of a well coordinated series of events that collectively constitute a primosomal cascade. Once the ring helicase is loaded, it recruits the primase and signals the switch to the polymerization mode. The transient nature of the helicase-primase (DnaB-DnaG) interaction in the Escherichia coli system has hindered our efforts to elucidate its structure and function. Taking advantage of the stable DnaB-DnaG complex in Bacillus stearothermophilus, we have reviewed conflicting mutagenic data from other bacterial systems and shown that DnaG interacts with the flexible linker that connects the N- and C-terminal domains of DnaB. Furthermore, atomic force microscopy (AFM) imaging experiments show that binding of the primase to the helicase induces predominantly a 3-fold symmetric morphology to the hexameric ring. Overall, three DnaG molecules appear to interact with the hexameric ring helicase but a small number of complexes with two and even one DnaG molecule bound to DnaB were also detected. The structural/functional significance of these data is discussed and a speculative structural model for this complex is suggested.

The helicase-primase interaction is a critical event in DNA replication and is mediated by a putative helicase-interaction domain within the primase. The solution structure of the helicase-interaction domain of DnaG reveals that it is made up of two independent subdomains: an N-terminal six-helix module and a C-terminal two-helix module that contains the residues of the primase previously identified as important in the interaction with the helicase. We show that the two-helix module alone is sufficient for strong binding between the primase and the helicase but fails to activate the helicase; both subdomains are required for helicase activation. The six-helix module of the primase has only one close structural homolog, the N-terminal domain of the corresponding helicase. This surprising structural relationship, coupled with the differences in surface properties of the two molecules, suggests how the helicase-interaction domain may perturb the structure of the helicase and lead to activation.

The acidic lipopeptides, including the calcium-dependent antibiotics (CDA), daptomycin, and A54145, are important macrocyclic peptide natural products produced by Streptomyces species. All three compounds contain a 3-methyl glutamate (3-MeGlu) as the penultimate C-terminal residue, which is important for bioactivity. Here, biochemical in vitro reconstitution of the 3-MeGlu biosynthetic pathway is presented, using exclusively enzymes from the CDA producer Streptomyces coelicolor. It is shown that the predicted 3-MeGlu methyltransferase GlmT and its homologues DptI from the daptomycin producer Streptomyces roseosporus and LptI from the A54145 producer Streptomyces fradiae do not methylate free glutamic acid, PCP-bound glutamate, or Glu-containing CDA in vitro. Instead, GlmT, DptI, and LptI are S-adenosyl methionine (SAM)-dependent alpha-ketoglutarate methyltransferases that catalyze the stereospecific methylation of alpha-ketoglutarate (alphaKG) leading to (3R)-3-methyl-2-oxoglutarate. Subsequent enzyme screening identified the branched chain amino acid transaminase IlvE (SCO5523) as an efficient catalyst for the transformation of (3R)-3-methyl-2-oxoglutarate into (2S,3R)-3-MeGlu. Comparison of reversed-phase HPLC retention time of dabsylated 3-MeGlu generated by the coupled enzymatic reaction with dabsylated synthetic standards confirmed complete stereocontrol during enzymatic catalysis. This stereospecific two-step conversion of alphaKG to (2S,3R)-3-MeGlu completes our understanding of the biosynthesis and incorporation of beta-methylated amino acids into the nonribosomal lipopeptides. Finally, understanding this pathway may provide new possibilities for the production of modified peptides in engineered microbes.