Lactose Binding to Galectin-1 Modulates Structural Dynamics, Increases Conformational Entropy, and Occurs with Apparent Negative Cooperativity.
J Mol Biol. 2010 Feb 22;
Authors: Nesmelova IV, Ermakova E, Daragan VA, Pang M, Menéndez M, Lagartera L, Solís D, Baum LG, Mayo KH
Galectins are a sub-family of lectins with a conserved carbohydrate recognition domain (CRD) that interacts with beta-galactosides. By binding cell surface glycoconjugates, galectin-1 (gal-1) is involved in cell adhesion and migration processes and is an important regulator of tumor angiogenesis. Here, we used heteronuclear NMR spectroscopy and molecular modeling to investigate lactose binding to gal-1 and to derive solution NMR structures of gal-1 in the lactose bound and unbound states. Structure analysis shows that the beta-strands and loops around the lactose binding site which are more open and dynamic in the unbound state, fold in around the bound lactose molecule dampening internal motions at that site and increasing motions elsewhere throughout the protein to contribute entropically to the binding free energy. CD data support the view of an overall more open structure in the lactose-bound state. Analysis of HSQC titration binding data indicates that lactose binds the two CRDs of the gal-1 dimer with negative cooperativity, in that the first lactose molecule binds more strongly (K(1) = 21 +/- 6 x10(3) M(-1)) than the second (K(2) = 4 +/- 2 x10(3) M(-1)). Isothermal calorimetry data fit using a sequential binding model present a similar picture, yielding K(1) = 20 +/- 10 x 10(3) M(-1) and K(2) = 1.67 +/- 0.07 x 10(3) M(-1). Molecular dynamics simulations provide insight into structural dynamics of the half-loaded lactose state and, together with NMR data, suggest that lactose binding at one site transmits a signal through the beta-sandwich and loops to the second binding site. Overall, our results provide new insight into gal-1 structure-function relationships and to protein-carbohydrate interactions in general.
PMID: 20184898 [PubMed - as supplied by publisher]
Structural and biochemical basis for the redox sensitivity of Mycobacterium tuberculosis RslA.
J Mol Biol. 2010 Feb 22;
Authors: Thakur KG, Praveena T, Gopal B
An effective transcriptional response to redox stimuli is of particular importance for Mycobacterium tuberculosis as it adapts to the environment of the host alveoli and the macrophage. The M. tuberculosis sigma factor sigma(L) regulates the expression of genes involved in cell wall and polyketide synthesis. sigma(L) interacts with the cytosolic anti-sigma domain (ASD) of a membrane-associated protein, RslA. Here we demonstrate that RslA binds Zn(2+)and can sequester sigma(L) in a reducing environment. In response to an oxidative stimulus, the proximal cysteines in the CXXC motif of RslA form a disulfide bond releasing the bound Zn(2+)ion. This results in a substantial rearrangement of the sigma(L)/RslA complex leading to an eight-fold decrease in the affinity of RslA for sigma(L). The crystal structure of the-35 element recognition domain of sigma(L), sigma(L)(4), bound to RslA reveals that RslA inactivates sigma(L) by sterically occluding promoter DNA and RNAP binding sites. The crystal structure further reveals that the cysteine residues that coordinate Zn(2+)in RslA are solvent exposed in the complex thus providing a structural basis for the redox sensitivity of RslA. The biophysical parameters of sigma(L)/RslA interactions provide a template to understand how variations in the rate of Zn(2+)release and associated conformational changes could regulate the activity of a Zn(2+)associated anti-sigma factor.
PMID: 20184899 [PubMed - as supplied by publisher]
Phospholipid demixing and the birth of a lipid droplet.
J Theor Biol. 2010 Feb 22;
Authors: Zanghellini J, Wodlei F, von Grünberg HH
The biogenesis of lipid droplets (LD) in the yeast Saccharomyces cerevisiae was theoretically investigated on basis of a biophysical model. In accordance with the prevailing model of LD formation, we assumed that neutral lipids oil-out between the membrane leaflets of the endoplasmic reticulum (ER), resulting in LD that bud-off when a critical size is reached. Mathematically, LD were modeled as spherical protuberances in an otherwise planar ER membrane. We estimated the local phospholipid composition, and calculated the change in elastic free energy of the membrane caused by nascent LD. Based on this model calculation, we found a gradual demixing of lipids in the membrane leaflet that goes along with an increase in surface curvature at the site of LD formation. During demixing, the phospholipid monolayer was able to gain energy during LD growth, which suggested that the formation of curved interfaces was supported by or even driven by lipid demixing. In addition, we show that demixing is thermodynamically necessary as LD cannot bud-off otherwise. In the case of Saccharomyces cerevisiae our model predicts a LD bud-off diameter of about 12 nm. This diameter is far below the experimentally determined size of typical yeast LD. Thus, we concluded that if the standard model of LD formation is valid, LD biogenesis is a two step process. Small LD are produced from the ER, which subsequently ripe within the cytosol through a series of fusions.
PMID: 20184900 [PubMed - as supplied by publisher]
Endemic disease, awareness, and local behavioural response.
J Theor Biol. 2010 Feb 22;
Authors: Funk S, Gilad E, Jansen VA
The spread of a contagious disease is often accompanied by a rise in awareness of those in the social vicinity of infected individuals, and a subsequent change in behaviour. Such reactions can manifest themselves in lower susceptibility as people try to prevent themselves from catching the disease, but also in lower infectivity because of self-imposed quarantine or better hygiene, shorter durations of infectiousness or longer immunity. We here focus on the scenario of an endemic disease of which members of the population can be either aware or unaware, and consider a broad set of possible reactions. We quantify the impact on the endemicity of a disease in a well-mixed population under the variation of different disease parameters as a consequence of growing awareness in the population. Applying a pair-closure scheme allows us to analyse the effect of local correlations if aware individuals tend to occur near infected cases, and to link this to the amount of overlap between the networks underlying the spread of awareness and disease, respectively. Lastly, we study the consequences on the dynamics when the pathogen and awareness spread at different velocities.
PMID: 20184901 [PubMed - as supplied by publisher]
Target size and optimal life history when individual growth and energy budget are stochastic.
J Theor Biol. 2010 Feb 22;
Authors: Filin I
I extend my previous work on life history optimization when body mass is divided into reserves and structure components. Two important innovations are: (1) effect of finite target size on optimal structural growth; (2) incorporating reproduction in the optimization objective. I derive optimal growth trajectories and life histories, given that the individual is subject to both starvation mortality and exogenous hazards (e.g., predation). Because of overhead costs in building structural mass, it is optimal to stop structural growth close to the target size, and to proceed only by accumulating reserves. Higher overhead costs cause earlier cessation of structural growth and smaller final structures. Semelparous reproduction also promotes early cessation of structural growth, compared to when only survival to target size is maximized. In contrast, iteroparous reproduction can prolong structural growth, resulting in larger final structures than in either the survival or the semelparous scenarios. Increasing the noise in individual growth lowers final structural mass at small target sizes, but the effect is reversed for large target sizes. My results provide predictions for comparative studies. I outline important consequences of my results to additional important evolutionary questions: evolution of sexual dimorphism, optimization of clutch size and evolution of progeny and adult sizes.
PMID: 20184902 [PubMed - as supplied by publisher]
High prevalence of multiple paternity in the invasive crayfish species, Procambarus clarkii.
Int J Biol Sci. 2010;6(1):107-15
Authors: Yue GH, Li JL, Wang CM, Xia JH, Wang GL, Feng JB
Reproductive strategy is a central feature of the ecology of invasive species as it determines the potential for population increase and range expansion. The red swamp crayfish, Procambarus clarkii, has invaded many countries and caused serious problems in freshwater ecosystems. However, little is known about the effects of environmental conditions on crayfish paternity and offspring traits in the wild. We studied these reproductive characteristics of P. clarkii in wild populations from two different habitats (ponds and ditches) in three locations with different environmental conditions in China. Genotyping of 1,436 offspring and 30 mothers of 30 broods was conducted by using four microsatellites. An analysis of genotyping results revealed that gravid females were the exclusive mother of the progeny they tended. Twenty-nine of 30 mothers had mated with multiple (2-4) males, each of which contributed differently to the number of offspring in a brood. The average number of fathers per brood and the number of offspring per brood were similar (P > 0.05) among six sampling sites, indicating that in P. clarkii multiple paternity and offspring number per brood are independent of environmental conditions studied. Indirect benefits from increasing the genetic diversity of broods, male and sperm competition, and cryptic female choice are a possible explanation for the high level multiple paternity and different contribution of fathers to offspring in this species.
Neural tube defects and impaired neural progenitor cell proliferation in Gbeta1-deficient mice.
Dev Dyn. 2010 Feb 23;
Authors: Okae H, Iwakura Y
Heterotrimeric G proteins are well known for their roles in signal transduction downstream of G protein-coupled receptors (GPCRs), and both Galpha subunits and tightly associated Gbetagamma subunits regulate downstream effector molecules. Compared to Galpha subunits, the physiological roles of individual Gbeta and Ggamma subunits are poorly understood. In this study, we generated mice deficient in the Gbeta1 gene and found that Gbeta1 is required for neural tube closure, neural progenitor cell proliferation, and neonatal development. About 40% Gbeta1(-/-) embryos developed neural tube defects (NTDs) and abnormal actin organization was observed in the basal side of neuroepithelium. In addition, Gbeta1(-/-) embryos without NTDs showed microencephaly and died within 2 days after birth. GPCR agonist-induced ERK phosphorylation, cell proliferation, and cell spreading, which were all found to be regulated by Galphai and Gbetagamma signaling, were abnormal in Gbeta1(-/-) neural progenitor cells. These data indicate that Gbeta1 is required for normal embryonic neurogenesis. Developmental Dynamics, 2010. (c) 2010 Wiley-Liss, Inc.
PMID: 20186915 [PubMed - as supplied by publisher]
Efficient transposition of a single Minos transposon copy in the genome of the ascidian Ciona intestinalis with a transgenic line expressing transposase in eggs.
Dev Dyn. 2010 Feb 23;
Authors: Hozumi A, Kawai N, Yoshida R, Ogura Y, Ohta N, Satake H, Satoh N, Sasakura Y
Transgenesis with transposons is an important technique for studying genetic functions. In the ascidian Ciona intestinalis, methods for germline transformation with the Tc1/mariner transposon Minos have been established. A system to remobilize a single Minos copy in the genome is needed to refine this transgenic technique. In this study, such an experimental system was established with a transgenic line expressing Minos transposase in eggs. In the eggs of a double transgenic animal from a cross between the egg transposase line and a transgenic line having a single Minos insertion, the transposon was transposed into new positions of the Ciona genome, thus creating new insertions. Some of the new insertions caused enhancer detection. The majority of the new insertion sites were mapped on different chromosomes from that of the transposon donor. This characteristic of Minos is in contrast to that of the Sleeping Beauty transposon, which causes frequent intrachromosomal transposition. Developmental Dynamics, 2010. (c) 2010 Wiley-Liss, Inc.
PMID: 20186916 [PubMed - as supplied by publisher]
Caenorhabditis elegans: A new model organism for studies of axon regeneration.
Dev Dyn. 2010 Feb 23;
Authors: Ghosh-Roy A, Chisholm AD
Axonal regeneration in Caenorhabditis elegans was first reported five years ago. Individual green fluorescent protein-labeled axons can be severed using laser microsurgery and their regrowth followed in vivo. Several neuron types display robust regrowth after injury, including motor and sensory neurons. The small size and transparency of C. elegans make possible large-scale genetic and pharmacological screens for regeneration phenotypes. Developmental Dynamics, 2010. (c) 2010 Wiley-Liss, Inc.
PMID: 20186917 [PubMed - as supplied by publisher]
Concordance Between Semiquantitative Immunohistochemical Assay and Oncotype DX RT-PCR Assay for Estrogen and Progesterone Receptors.
Appl Immunohistochem Mol Morphol. 2010 Feb 24;
Authors: Oʼconnor SM, Beriwal S, Dabbs DJ, Bhargava R
Estrogen receptor (ER) status is a strong predictor of response to hormonal therapy in women with breast cancer. Not only presence of ER, but also level of expression has been shown to correlate with time to recurrence in patients undergoing therapy with tamoxifen or anastrozole. In addition, risk reduction occurs in ER-negative, progesterone receptor (PR)-positive patients treated with hormonal therapy. Immunohistochemistry (IHC) has been the method of choice for determining hormone receptor status. Recently, Genomic Health began reporting ER and PR status measured quantitatively by reverse transcription-polymerase chain reaction (RT-PCR) as a component of its Oncotype DX assay. As part of our quality assurance program, we reviewed 80 breast cancer cases that had been evaluated by the Oncotype DX assay and also underwent immunohistochemical staining for ER and PR. We found excellent correlation between ER and PR status determined qualitatively by each method. In addition, when hormone receptor expression measured quantitatively by RT-PCR and semiquantitatively by IHC were compared, results showed linear correlation. Given the additional advantages of hormone receptor IHC performed on intact tissue sections, currently there is no definitive reason to switch to RT-PCR for determination of ER and PR expressions.
PMID: 20186046 [PubMed - as supplied by publisher]
