Lipidomics of homeoviscous adaptation to low temperatures in Staphylococcus aureus utilizing exogenous straight-chain unsaturated fatty acids.

It is well established that Staphylococcus aureus can incorporate exogenous straight-chain unsaturated fatty acids (SCUFAs) into membrane phospho- and glyco-lipids from various sources in supplemented culture media and when growing in vivo during infection. Given the enhancement of membrane fluidity when oleic acid (C18:1Δ9) is incorporated into lipids, we were prompted to examine the effect of medium supplementation with C18:1Δ9 on growth at low temperatures. C18:1Δ9 supported the growth of a cold-sensitive, branched-chain fatty acid (BCFA)-deficient mutant at 12°C. Interestingly, we found similar results in the BCFA-sufficient parental strain, supported by the fact that the incorporation of C18:1Δ9 into the membrane increased membrane fluidity in both strains. We show that the incorporation of C18:1Δ9 and its elongation product C20:1Δ11 into membrane lipids was required for growth stimulation and relied on a functional FakAB incorporation system. Lipidomics analysis of the phosphatidylglycerol and diglycosyldiacylglycerol lipid classes revealed major impacts of C18:1Δ9 and temperature on lipid species. Growth at 12°C in the presence of C18:1Δ9 also led to increased production of the carotenoid pigment staphyloxanthin. The enhancement of growth by C18:1Δ9 is an example of homeoviscous adaptation to low temperatures utilizing an exogenous fatty acid. This may be significant in the growth of S. aureus at low temperatures in foods that commonly contain C18:1Δ9 and other SCUFAs in various forms. IMPORTANCE: We show that Staphylococcus aureus can use its known ability to incorporate exogenous fatty acids to enhance its growth at low temperatures. Individual species of phosphatidylglycerols and diglycosyldiacylglycerols bearing one or two degrees of unsaturation derived from the incorporation of C18:1Δ9 at 12°C are described for the first time. In addition, enhanced production of the carotenoid staphyloxanthin occurs at low temperatures. The studies describe a biochemical reality underlying membrane biophysics. This is an example of homeoviscous adaptation to low temperatures utilizing exogenous fatty acids over the regulation of the biosynthesis of endogenous fatty acids. The studies have likely relevance to food safety in that unsaturated fatty acids may enhance the growth of S. aureus in the food environment.

Lipidomics of homeoviscous adaptation to low temperatures in Staphylococcus aureus utilizing exogenous straight-chain unsaturated fatty acids over biosynthesized endogenous branched-chain fatty acids.

It is well established that Staphylococcus aureus can incorporate exogenous straight-chain unsaturated fatty acids (SCUFAs) into membrane phospho- and glyco-lipids from various sources in supplemented culture media, and when growing in vivo in an infection. Given the enhancement of membrane fluidity when oleic acid (C18:1Δ9) is incorporated into lipids, we were prompted to examine the effect of medium supplementation with C18:1Δ9 on growth at low temperatures. C18:1Δ9 supported the growth of a cold-sensitive, branched-chain fatty acid (BCFA)-deficient mutant at 12°C. Interestingly, we found similar results in the BCFA-sufficient parental strain. We show that incorporation of C18:1Δ9 and its elongation product C20:1Δ9 into membrane lipids was required for growth stimulation and relied on a functional FakAB incorporation system. Lipidomics analysis of the phosphatidylglycerol (PG) and diglycosyldiacylglycerol (DGDG) lipid classes revealed major impacts of C18:1Δ9 and temperature on lipid species. Growth at 12°C in the presence of C18:1Δ9 also led to increased production of the carotenoid pigment staphyloxanthin; however, this was not an obligatory requirement for cold adaptation. Enhancement of growth by C18:1Δ9 is an example of homeoviscous adaptation to low temperatures utilizing an exogenous fatty acid. This may be significant in the growth of S. aureus at low temperatures in foods that commonly contain C18:1Δ9 and other SCUFAs in various forms.

A Na pump with reduced stoichiometry is up-regulated by brine shrimp in extreme salinities.

Brine shrimp (Artemia) are the only animals to thrive at sodium concentrations above 4 M. Salt excretion is powered by the Na+,K+-ATPase (NKA), a heterodimeric (αß) pump that usually exports 3Na+ in exchange for 2 K+ per hydrolyzed ATP. Artemia express several NKA catalytic α-subunit subtypes. High-salinity adaptation increases abundance of α2KK, an isoform that contains two lysines (Lys308 and Lys758 in transmembrane segments TM4 and TM5, respectively) at positions where canonical NKAs have asparagines (Xenopus α1's Asn333 and Asn785). Using de novo transcriptome assembly and qPCR, we found that Artemia express two salinity-independent canonical α subunits (α1NN and α3NN), as well as two ß variants, in addition to the salinity-controlled α2KK. These ß subunits permitted heterologous expression of the α2KK pump and determination of its CryoEM structure in a closed, ion-free conformation, showing Lys758 residing within the ion-binding cavity. We used electrophysiology to characterize the function of α2KK pumps and compared it to that of Xenopus α1 (and its α2KK-mimicking single- and double-lysine substitutions). The double substitution N333K/N785K confers α2KK-like characteristics to Xenopus α1, and mutant cycle analysis reveals energetic coupling between these two residues, illustrating how α2KK's Lys308 helps to maintain high affinity for external K+ when Lys758 occupies an ion-binding site. By measuring uptake under voltage clamp of the K+-congener 86Rb+, we prove that double-lysine-substituted pumps transport 2Na+ and 1 K+ per catalytic cycle. Our results show how the two lysines contribute to generate a pump with reduced stoichiometry allowing Artemia to maintain steeper Na+ gradients in hypersaline environments.

Structure and activity of native and thiolated α-chymotrypsin adsorbed onto gold nanoparticles.

A detailed understanding of protein-nanoparticle interactions is critical to realize the full potential of bioconjugate-enabled technologies. Parameters that lead to conformational changes in protein structure upon adsorption must be identified and controlled to mitigate loss of biological function. We hypothesized that the installation of thiol functional groups on a protein will facilitate robust adsorption to gold nanoparticles (AuNPs) and prevent protein unfolding to achieve thermodynamic stability. Here we investigated the adsorption behavior of α-chymotrypsin (ChT) and a thiolated analog of α-chymotrypsin (T-ChT) with AuNPs. ChT, which does not present any free thiols, was modified with 2-iminothiolane (Traut's reagent) to synthesize T-ChT consisting of two free thiols. Protein adsorption to AuNPs was monitored with dynamic light scattering and UV-vis spectrophotometry, and fluorescence spectra were acquired to assess changes in protein structure induced by interaction with the AuNP. The biological function of ChT, T-ChT, and respective bioconjugates were compared using a colorimetric enzymatic assay. The thiolated analog exhibited a greater affinity for the AuNP than the unmodified ChT, as determined from adsorption isotherms. The ChT protein formed a soft protein corona in which the enzyme denatures with prolonged exposure to AuNPs and, subsequently, lost enzymatic function. Conversely, the T-ChT formed a robust hard corona on the AuNP and retained structure and function. These data support the hypothesis, provide further insight into protein-AuNP interactions, and identify a simple chemical approach to synthesize robust and functional conjugates.

A Dual-Pronged Approach: A Ruthenium(III) Complex That Modulates Amyloid-ß Aggregation and Disrupts Its Formed Aggregates.

Alzheimer's disease (AD) is a devastating neurological disorder for which soluble oligomers of the peptide amyloid-ß (Aß) are now recognized as the neurotoxic species. Metal-based therapeutics are uniquely suited to target Aß, with ruthenium-based (Ru) complexes emerging as propitious candidates. Recently, azole-based Ru(III) complexes were observed to modulate the aggregation of Aß in solution, where the inclusion of a primary amine proximal to the ligand coordination site improved the activity of the complexes. To advance these structure-activity relationships, a series of oxazole-based Ru complexes were prepared and evaluated for their ability to modulate Aß aggregation. From these studies, a lead candidate, Oc, emerged that had superior activity relative to its azole predecessors in modulating the aggregation of soluble Aß and diminishing its cytotoxicity. Further evaluation of Oc demonstrated its ability to disrupt formed Aß aggregates, resulting in smaller amorphous species. Because altering both sides of the aggregation equilibrium for Aß has not been previously suggested for metal-based complexes for AD, this work represents an exciting new avenue for improved therapeutic success.