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Calcium ions (Ca(2+)) modulate the phototransduction cascade of vertebrate cone photoreceptors to tune gain, inactivation, and light adaptation. In darkness, the continuous current entering the cone outer segment through cGMP-gated (CNG) channels is carried in part by Ca(2+), which is then extruded back to the extracellular space. The mechanism of Ca(2+) extrusion from mammalian cones is not understood. The dominant view has been that the cone-specific isoform of the Na(+)/Ca(2+), K(+) exchanger, NCKX2, is responsible for removing Ca(2+) from their outer segments. However, indirect evaluation of cone function in NCKX2-deficient (Nckx2(-/-)) mice by electroretinogram recordings revealed normal photopic b-wave responses. This unexpected result suggested that NCKX2 may not be involved in the Ca(2+) homeostasis of mammalian cones. To address this controversy, we examined the expression of NCKX2 in mouse cones and performed transretinal recordings from Nckx2(-/-) mice to determine the effect of NCKX2 deletion on cone function directly. We found that Nckx2(-/-) cones exhibit compromised phototransduction inactivation, slower response recovery and delayed background adaptation. We conclude that NCKX2 is required for the maintenance of efficient Ca(2+) extrusion from mouse cones. However, surprisingly, Nckx2(-/-) cones adapted normally in steady background light, indicating the existence of additional Ca(2+)-extruding mechanisms in mammalian cones.

Cone photoreceptors function under daylight conditions and are essential for color perception and vision with high temporal and spatial resolution. A remarkable feature of cones is that, unlike rods, they remain responsive in bright light. In rods, light triggers a decline in intracellular calcium, which exerts a well studied negative feedback on phototransduction that includes calcium-dependent inhibition of rhodopsin kinase (GRK1) by recoverin. Rods and cones share the same isoforms of recoverin and GRK1, and photoactivation also triggers a calcium decline in cones. However, the molecular mechanisms by which calcium exerts negative feedback on cone phototransduction through recoverin and GRK1 are not well understood. Here, we examined this question using mice expressing various levels of GRK1 or lacking recoverin. We show that although GRK1 is required for the timely inactivation of mouse cone photoresponse, gradually increasing its expression progressively delays the cone response recovery. This surprising result is in contrast with the known effect of increasing GRK1 expression in rods. Notably, the kinetics of cone responses converge and become independent of GRK1 levels for flashes activating more than ∼1% of cone pigment. Thus, mouse cone response recovery in bright light is independent of pigment phosphorylation and likely reflects the spontaneous decay of photoactivated visual pigment. We also find that recoverin potentiates the sensitivity of cones in dim light conditions but does not contribute to their capacity to function in bright light.

Since daily dietary habits can affect cognitive function, dietary patterns such as the Mediterranean-DASH Intervention for Neurodegenerative Delay diet have been proposed as interventions to slow cognitive decline. However, because dietary habits vary widely among different food cultures, it is necessary to establish dietary pattern intervention methods that are appropriate for each population. Therefore, in this study, the dietary patterns of elderly Japanese individuals were classified using cluster analysis, and their relationship with cognitive function was investigated. We then modeled the dietary patterns and applied them to another cohort of elderly Japanese individuals to determine whether differences in dietary patterns could predict cognitive decline. One hundred and fifty older adults ≥ 65 years of age in the community were recruited. Their daily food intake and cognitive function were measured using the brief-type self-administered diet history questionnaire and Montreal Cognitive Assessment, respectively. K-means cluster analysis identified a high-carbohydrate (HC) dietary pattern with high cereal intake and a protein-balanced (PB) dietary pattern with high intake of legumes, vegetables, seafood, meat, and eggs. Cognitive function was significantly higher in the PB group than in the HC group. Furthermore, to classify the new data into HC and PB patterns, a classification model was created by discriminant analysis using food groups with significantly different intakes among dietary patterns. Next, we recruited 267 new older adults ≥ 65 years of age and measured food intake and cognitive function assessed using the memory performance index score. Individuals with cognitive decline were identified and their detailed cognitive functions were assessed using the neurocognitive index score. Cognitive function was significantly impaired in the HC pattern in both the general elderly and cognitively impaired cohorts. These findings suggest that a dietary pattern of low carbohydrate and high protein intake is associated with good cognitive function in elderly Japanese individuals. Classification by these dietary patterns can predict cognitive reservation in community-dwelling older adults. [ABSTRACT FROM AUTHOR]

The multidrug efflux transporter AcrB and its homologues are important in the multidrug resistance of Gram-negative pathogens (1,2). However, despite efforts to develop efflux inhibitors (3), clinically useful inhibitors are not available at present (4,5). Pyridopyrimidine derivatives are AcrB- and MexB-specific inhibitors that do not inhibit MexY (6,7); MexB and MexY are principal multidrug exporters in Pseudomonas aeruginosa (8-10). We have previously determined the crystal structure of AcrB in the absence and presence of antibiotics (11-13). Drugs were shown to be exported by a functionally rotating mechanism (12) through tandem proximal and distal multisite drug-binding pockets (13). Here we describe the first inhibitor-bound structures of AcrB and MexB, in which these proteins are bound by a pyridopyrimidine derivative. The pyridopyrimidine derivative binds tightly to a narrow pit composed of a phenylalanine cluster located in the distal pocket and sterically hinders the functional rotation. This pit is a hydrophobic trap that branches off from the substrate-translocation channel. Phe 178 is located at the edge of this trap in AcrB and MexB and contributes to the tight binding of the inhibitor molecule through a π-π interaction with the pyridopyrimidine ring. The voluminous side chain of Trp 177 located at the corresponding position in MexY prevents inhibitor binding. The structure of the hydrophobic trap described in this study will contribute to the development of universal inhibitors of MexB and MexY in P. aeruginosa., Members of the resistance-nodulation-division (RND) family of transporters, which include AcrB, are tripartite complexes composed of an inner membrane transporter, a membrane fusion protein and an outer membrane channel (14,15). [...]

AcrB and its homologues are the principal multidrug transporters in Gram-negative bacteria (1-6) and are important in antibiotic drug tolerance (7,8). AcrB is a homotrimer that acts as a tripartite [...]

Rod and cone photoreceptors use similar but distinct sets of phototransduction proteins to achieve different functional properties, suitable for their role as dim and bright light receptors, respectively. For example, rod and cone visual pigments couple to distinct variants of the heterotrimeric G protein transducin. However, the role of the structural differences between rod and cone transducin [alpha] subunits (T[alpha]) in determining the functional differences between rods and cones is unknown. To address this question, we studied the translocation and signaling properties of rod T[alpha] expressed in cones and cone T[alpha] expressed in rods in three mouse strains: rod T[alpha] knockout, cone T[alpha] [GNAT2.sup.cpfl3] mutant, and rod and cone T[alpha] double mutant rd17 mouse. Surprisingly, although the rod/cone T[alpha] are only 79% identical, exogenously expressed rod or cone T[alpha] localized and translocated identically to endogenous T[alpha] in each photoreceptor type. Moreover, exogenously expressed rod or cone T[alpha] rescued electroretinogram responses (ERGs) in mice lacking functional cone or rod T[alpha], respectively. Ex vivo transretinal ERG and single-cell recordings from rd17 retinas treated with rod or cone T[alpha] showed comparable rod sensitivity and response kinetics. These results demonstrate that cone T[alpha] forms a functional heterotrimeric G protein complex in rods and that rod and cone T[alpha] couple equally well to the rod phototransduction cascade. Thus, rod and cone transducin [alpha]-subunits are functionally interchangeable and their signaling properties do not contribute to the intrinsic light sensitivity differences between rods and cones. Additionally, the technology used here could be adapted for any such homoIogue swap desired. photoreceptor | phototransduction | signaling property | translocation doi/ 10.1073/pnas.0901382106

Rod and cone photoreceptor cells that are responsible for scotopic and photopic vision, respectively, exhibit photoresponses different from each other and contain similar phototransduction proteins with distinctive molecular properties. To investigate the contribution of the different molecular properties of visual pigments to the responses of the photoreceptor cells, we have generated knock-in mice in which rod visual pigment (rhodopsin) was replaced with mouse green-sensitive cone visual pigment (mouse green). The mouse green was successfully transported to the rod outer segments, though the expression of mouse green in homozygous retina was ~11% of rhodopsin in wild-type retina. Single-cell recordings of wild-type and homozygous rods suggested that the flash sensitivity and the single-photon responses from mouse green were three to fourfold lower than those from rhodopsin after correction for the differences in cell volume and levels of several signal transduction proteins. Subsequent measurements using heterozygous rods expressing both mouse green and rhodopsin E122Q mutant, where these pigments in the same rod cells can be selectively irradiated due to their distinctive absorption maxima, clearly showed that the photoresponse of mouse green was threefold lower than that of rhodopsin. Noise analysis indicated that the rate of thermal activations of mouse green was 1.7 X [10.sup.7] [s.sup.-1], about 860-told higher than that of rhodopsin. The increase in thermal activation of mouse green relative to that of rhodopsin results in only 4% reduction of rod photosensitivity for bright lights, but would instead be expected to severely affect the visual threshold under dim-light conditions. Therefore, the abilities of rhodopsin to generate a large single photon response and to retain high thermal stability in darkness are factors that have been necessary for the evolution of scotopic vision.

The total synthesis of cytotoxic marine phosphomacrolides, (−)‐enigmazole A and (−)‐15‐O‐methylenigmazole A, is described in detail. The 2,6‐cis‐substituted tetrahydropyran ring was efficiently elaborated by using a tandem olefin cross‐metathesis/intramolecular oxa‐Michael addition reaction. The 18‐membered macrolactone skeleton was forged via a Au‐catalyzed propargylic benzoate rearrangement/macrocyclic ring‐closing metathesis sequence. Late‐stage diversification of a common intermediate enabled unified total synthesis of (−)‐enigmazole A and (−)‐15‐O‐methylenigmazole A. [ABSTRACT FROM AUTHOR]

The structure, physicochemical property and reactivity of the reconstituted protein are described in order to evaluate the role of the 7-propionate side chain in the native protein. The studies have shown that the 7-propionate side chain has functioned not only as a water gate to repel water molecules from bulk to promote the high d-camphor affinity but also as a pivot in the hydrogen-bonding tetrad to regulate the water expulsion system at the initial step of P450cam catalyst cycle.

Total synthesis of (−)‐enigmazole A, a marine macrolide natural product with cytotoxic activity, has been accomplished. The tetrahydropyran moiety was constructed by means of a domino olefin cross‐metathesis/intramolecular oxa‐Michael addition of a δ‐hydroxy olefin. After coupling of advanced intermediates, the macrocycle was formed through gold‐catalyzed rearrangement of a propargylic benzoate, followed by ring‐closing metathesis of the resultant α,β‐unsaturated ketone. [ABSTRACT FROM AUTHOR]