Protein engineering of class-A non-specific acid phosphatase (PhoN) of Salmonella typhimurium: modulation of the pH-activity profile

An Unexpected Role for the Periplasmic Phosphatase PhoN in the Salvage of B6 Vitamers in Salmonella enterica

Pyridoxal 5'-phosphate (PLP) is the biologically active form of vitamin B₆, essential for cellular function in all domains of life. In many organisms, such as Salmonella enterica serovar Typhimurium and Escherichia coli, this cofactor can be synthesized de novo or salvaged from B₆ vitamers in the environment. Unexpectedly, S. enterica strains blocked in PLP biosynthesis were able to use exogenous PLP and pyridoxine 5'-phosphate (PNP) as the source of this required cofactor, while E. coli strains of the same genotype could not. Transposon mutagenesis found that phoN was essential for the salvage of PLP and PNP under the conditions tested. phoN encodes a class A nonspecific acid phosphatase (EC 3.1.3.2) that is transcriptionally regulated by the PhoPQ two-component system. The periplasmic location of PhoN was essential for PLP and PNP salvage, and in vitro assays confirmed PhoN has phosphatase activity with PLP and PNP as substrates. The data suggest that PhoN dephosphorylates B₆ vitamers, after which they enter the cytoplasm and are phosphorylated by kinases of the canonical PLP salvage pathway. The connection of phoN with PhoPQ and the broad specificity of the gene product suggest S. enterica is exploiting a moonlighting activity of PhoN for PLP salvage.IMPORTANCE Nutrient salvage is a strategy used by species across domains of life to conserve energy. Many organisms are unable to synthesize all required metabolites de novo and must rely exclusively on salvage. Others supplement de novo synthesis with the ability to salvage. This study identified an unexpected mechanism present in S. enterica that allows salvage of phosphorylated B₆ vitamers. In vivo and in vitro data herein determined that the periplasmic phosphatase PhoN can facilitate the salvage of PLP and PNP. We suggest a mechanistic working model of PhoN-dependent utilization of PLP and PNP and discuss the general role of promiscuous phosphatases and kinases in organismal fitness.

An Artificial Pathway for Isoprenoid Biosynthesis Decoupled from Native Hemiterpene Metabolism

Isoprenoids are constructed in nature using hemiterpene building blocks that are biosynthesized from lengthy enzymatic pathways with little opportunity to deploy precursor-directed biosynthesis. Here, an artificial alcohol-dependent hemiterpene biosynthetic pathway was designed and coupled to several isoprenoid biosynthetic systems, affording lycopene and a prenylated tryptophan in robust yields. This approach affords a potential route to diverse non-natural hemiterpenes and by extension isoprenoids modified with non-natural chemical functionality. Accordingly, the prototype chemo-enzymatic pathway is a critical first step toward the construction of engineered microbial strains for bioconversion of simple scalable building blocks into complex isoprenoid scaffolds.

Phylogenetic distribution, biogeography and the effects of land management upon bacterial non-specific Acid phosphatase Gene diversity and abundance

BACKGROUND AND AIMS

Bacterial Non-Specific Acid Phosphatase (NSAP) enzymes are capable of dephosphorylating diverse organic phosphoesters but are rarely studied: their distribution in natural and managed environments is poorly understood. The aim of this study was to generate new insight into the environmental distribution of NSAPs and establish their potential global relevance to cycling of organic phosphorus.

METHODS

We employed bioinformatic tools to determine NSAP diversity and subcellular localization in microbial genomes; used the corresponding NSAP gene sequences to census metagenomes from diverse ecosystems; studied the effect of long-term land management upon NSAP diversity and abundance.

RESULTS

Periplasmic class B NSAPs are poorly represented in marine and terrestrial environments, reflecting their association with enteric and pathogenic bacteria. Periplasmic class A and outer membrane-associated class C NSAPs are cosmopolitan. NSAPs are more abundant in marine than terrestrial ecosystems and class C more abundant than class A genes, except in an acidic peat where class A genes dominate. A clear effect of land management upon gene abundance was identified.

CONCLUSIONS

NSAP genes are cosmopolitan. Class C genes are more widely distributed: their association with the outer-membrane of cells gives them a clear role in the cycling of organic phosphorus, particularly in soils.

Variant of the Thermomyces lanuginosus lipase with improved kinetic stability: a candidate for enzyme replacement therapy

Lipases with high kinetic stability and enzymatic efficiency in the human gastro-intestinal tract may help against exocrine pancreatic insufficiency. Here we mimic gastric conditions to study how bile salts and pH affect the stability and activity of Thermomyces lanuginosus lipase (TlL) and its stabler variant StL using spectroscopy, calorimetry and gel electrophoresis. Both enzymes resist trypsin digestion with and without bile salts. Bile salts activate native TlL and StL equally well, bind weakly to denatured TlL and StL at lower pH and precipitate native TlL and StL at pH 4. StL refolds more efficiently than TlL from gastric pH in bile salts, regaining activity when refolding from pH as low as 1.8 and above while TlL cannot go below pH 2.6. StL also unfolds 10-40 fold more slowly in the denaturant guanidinium chloride and the anionic surfactant SDS. We ascribe StL's superior performance to general alterations in its electrostatic potential which makes it more acid-resistant. These superior properties make StL a good candidate for pancreatic enzyme replacement therapy.

Directed evolution of a lysosomal enzyme with enhanced activity at neutral pH by mammalian cell-surface display

Human beta-glucuronidase, due to low intrinsic immunogenicity in humans, is an attractive enzyme for tumor-specific prodrug activation, but its utility is hindered by low activity at physiological pH. Here we describe the development of a high-throughput screening procedure for enzymatic activity based on the stable retention of fluorescent reaction product in mammalian cells expressing properly folded glycoproteins on their surface. We utilized this procedure on error-prone PCR and saturation mutagenesis libraries to isolate beta-glucuronidase tetramers that were up to 60-fold more active (k(cat)/K(m)) at pH 7.0 and were up to an order of magnitude more effective at catalyzing the conversion of two structurally disparate glucuronide prodrugs to anticancer agents. The screening procedure described here can facilitate investigation of eukaryotic enzymes requiring posttranslational modifications for biological activity.