Active calcium transport via coupling between the enzymatic and the ionophoric sites of Ca2+ + Mg2+-ATPase

The 20K dalton fragment of Ca²⁺ + Mg²⁺-ATPase obtained from the tryptically digested sarcoplasmic reticulum has been further purified using Bio-Gel P-100. This removed low-molecular-weight UV-absorbing and positive Lowry-reacting contaminants. The ionophoric activity of the 20K fragment in both oxidized cholesterol and phosphatidylcholine: cholesterol membranes is unaltered by this further purification. The 20K selectivity sequence in phosphatidylcholine: cholesterol membranes is Ba²⁺ > Ca²⁺ > Sr²⁺ > Mn²⁺ Mg²⁺. Digestion of intact sarcoplasmic reticulum vesicles with trypsin, which results in the dissection of the hydrolytic site (30K) from the ionophoric site (20K), is shown to disrupt energy transduction between ATP hydrolysis and calcium transport. This further implicates the 20K dalton fragment as a calcium transport site. These data and previous evidence are discussed in terms of a proposed model for the ATPase molecular structure and the mechanism of cation transport in sarcoplasmic reticulum.     

Solvent perturbation evidence for a two-state system regulated by calcium in sarcoplasmic reticulum ATPase

Perturbation of sarcoplasmic reticulum ATPase with the nonionic detergent C12E8 is modulated by the amount of free Ca2+ present in the solvent prior to the addition of detergent. CD measurements show that the enzyme exists in solution in two different conformations that react differently with the detergent. They probably represent the free enzyme, and its complex with Ca2+. On this assumption, titrations with increasing amounts of Ca2+ produced data superimposable on curves obtained measuring Ca2+ bound to sarcoplasmic reticulum vesicles.     

EfgA is a conserved formaldehyde sensor that leads to bacterial growth arrest in response to elevated formaldehyde

Normal cellular processes give rise to toxic metabolites that cells must mitigate. Formaldehyde is a universal stressor and potent metabolic toxin that is generated in organisms from bacteria to humans. Methylotrophic bacteria such as Methylorubrum extorquens face an acute challenge due to their production of formaldehyde as an obligate central intermediate of single-carbon metabolism. Mechanisms to sense and respond to formaldehyde were speculated to exist in methylotrophs for decades but had never been discovered. Here, we identify a member of the DUF336 domain family, named efgA for enhanced formaldehyde growth, that plays an important role in endogenous formaldehyde stress response in M. extorquens PA1 and is found almost exclusively in methylotrophic taxa. Our experimental analyses reveal that EfgA is a formaldehyde sensor that rapidly arrests growth in response to elevated levels of formaldehyde. Heterologous expression of EfgA in Escherichia coli increases formaldehyde resistance, indicating that its interaction partners are widespread and conserved. EfgA represents the first example of a formaldehyde stress response system that does not involve enzymatic detoxification. Thus, EfgA comprises a unique stress response mechanism in bacteria, whereby a single protein directly senses elevated levels of a toxic intracellular metabolite and safeguards cells from potential damage.

The known formaldehyde stress response systems involve enzymatic detoxification. Here, the authors show that the formaldehyde sensor efgA plays an important role in the endogenous formaldehyde stress response in Methylorubrum extorquens, halting cell growth in response to elevated levels of formaldehyde, and is found almost exclusively in methylotrophic taxa.     

Synthesis of the allo-analogue of trehalose

Selective benzoylation of HO-2 and HO-2′ of 4,6-O-benzylidene-α-D-glucopyranosyl 4,6-O-benzylidene-α-D-glucopyranoside with N-benzoylimidazole led to the exclusive formation of 2-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranosyl 2-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranoside. Oxidation of either the dibenzoate or the corresponding ditosylate with methyl sulphoxide-phosphorus pentaoxide gave the 3,3′-diulose, and subsequent reduction with borohydride gave the 3,3′diepimers having the allo-allo configuration. De-esterification and hydrolysis of the benzylidene substituents gave α-D-allopyranosyl α-D-allopyranoside.