Phosphatidylserine (PS) is a relatively minor constituent of biological membranes. Despite its low abundance, PS in the plasma membrane (PM) plays key roles in various phenomena such as the coagulation cascade, clearance of apoptotic cells, and recruitment of signaling molecules. PS also localizes in endocytic organelles, but how this relates to its cellular functions remains unknown. Here we report that PS is essential for retrograde membrane traffic at recycling endosomes (REs). PS was most concentrated in REs among intracellular organelles, and evectin-2 (evt-2), a protein of previously unknown function, was targeted to REs by the binding of its pleckstrin homology (PH) domain to PS. X-ray analysis supported the specificity of the binding of PS to the PH domain. Depletion of evt-2 or masking of intracellular PS suppressed membrane traffic from REs to the Golgi. These findings uncover the molecular basis that controls the RE-to-Golgi transport and identify a unique PH domain that specifically recognizes PS but not polyphosphoinositides. cholera toxin | endocytosis

Dipeptidyl peptidase IV (DPP-4) enzyme is responsible for the degradation of incretins that stimulates insulin secretion and hence inhibition of DPP-4 becomes an established approach for the treatment of type 2 diabetics. We studied the interaction between DPP-4 and its inhibitor drugs (sitagliptin 1, linagliptin 2, alogliptin 3, and teneligliptin 4) quantitatively by using fragment molecular orbital calculations at the RI-MP2/cc-pVDZ level to analyze the inhibitory activities of the drugs. Apart from having common interactions with key residues, inhibitors encompassing the DPP-4 active site extensively interact widely with the hydrophobic pocket by their hydrophobic inhibitor moieties. The cumulative hydrophobic interaction becomes stronger for these inhibitors and hence linagliptin and teneligliptin have larger interaction energies, and consequently higher inhibitory activities, than their alogliptin and sitagliptin counterparts. Though effective interaction for both 2 and 3 is at subsite, 2 has a stronger binding to this subsite interacting with Trp629 and Tyr547 than 3 does. The presence of triazolopiperazine and piperazine moiety in 1 and 4, respectively, provides the interaction to the S2 extensive subsite; however, the latter’s superior inhibitory activity is not only due to a relatively tighter binding to the S2 extensive subsite, but also due to the interactions to the S1 subsite. The calculated hydrophobic interfragment interaction energies correlate well with the experimental binding affinities (KD) and inhibitory activities (IC50) of the DPP-4 inhibitors.

The first ("by definition") cyanide-free enantioselective synthetic approach towards chiral aand b-branched nitriles is reported. This process is based on a biocatalytic dehydration of racemic aldoximes by using an aldoxime dehydratase and proceeds with high conversion and excellent enantioselectivity (up to 98 % ee) with water as the only side-product when starting from a racemic substrate with a high E/Z ratio. Thus, in combination with the facile generation of aldoximes through condensation of readily accessible aldehydes with hydroxylamine, this methodology offers an attractive and efficient path to chiral nitriles with excellent atom economy in aqueous solution. Furthermore, this study shows a surprising enzymatic dependency of the enantiopreference on the E or Z configuration of the aldoxime moiety. Notably, the whole stereochemical course of this enzymatic reaction has been rationalized by means of a computational study.From the early days of organic chemistry, (chiral) nitriles have been widely used as versatile intermediates in the synthesis of carboxylic acids (by hydrolysis) and amines (by hydrogenation). [1] A selected recent example underlining the importance of chiral nitrile intermediates is the synthesis of boceprevir (Merck) as a drug for treatment of hepatitis C. [2] Furthermore, recently chiral a-branched nitrile motifs have increasingly been part of the key structural framework in novel final drug molecules that have already been clinically approved, such as vildagliptin (Novartis) and saxagliptin (Bristol Myers Squibb). [3,4] Thus, the search for efficient enantioselective synthetic strategies towards chiral nitriles has gained tremendous significance for organic chemists and the pharmaceutical industry. Hitherto, the preferred introduction of a chiral nitrile moiety into a molecule has proceeded through reactions with cyanide (either by substitution or addition reactions). Besides using cy-anide in the synthesis of racemic or prochiral substrates for subsequent resolutions [5][6][7] or asymmetric reactions [8][9][10] with the formed nitriles, a range of asymmetric catalytic cyanations have been developed. [11][12][13][14][15][16] Cyanide, however, is highly toxic and there is a strong demand for developing methods that avoid the use of cyanide in the asymmetric or preceding synthetic steps for the nitrile substrates. Ideally, such alternative methods should also be attractive for applications on the industrial scale. Notably, until now there has not been a single asymmetric method for synthesizing a-branched chiral nitriles that "by definition" does not rely on the use of cyanide: for existing routes cyanide is either required or conceivably used in the substrate synthesis (if chiral, racemic, or prochiral nitriles serve as substrates) or in the enantioselective step (through enantioselective cyanation reactions).Looking at Nature's way to prepare nitriles, which notably are found in several natural products, [17] we became inspired to use enzymes for the enantioselective synthesis of chiral...

We have determined the x-ray crystal structure of L-lysine ε-oxidase from Marinomonas mediterranea in its native and L-lysine-complex forms at 1.94- and 1.99-Å resolution, respectively. In the native enzyme, electron densities clearly indicate the presence of cysteine tryptophylquinone (CTQ) previously identified in quinohemoprotein amine dehydrogenase. In the L-lysine-complex, an electron density corresponding to the bound L-lysine shows that its ε-amino group is attached to the C6 carbonyl group of CTQ, suggesting the formation of a Schiff-base intermediate. Collectively, the present crystal structure provides the first example of an enzyme employing a tryptophylquinone cofactor in an amine oxidase.