Insights into Coupled Folding and Binding Mechanisms from Kinetic Studies

Intrinsically disordered proteins (IDPs) are characterized by a lack of persistent structure. Since their identification more than a decade ago, many questions regarding their functional relevance and interaction mechanisms remain unanswered. Although most experiments have taken equilibrium and structural perspectives, fewer studies have investigated the kinetics of their interactions. Here we review and highlight the type of information that can be gained from kinetic studies. In particular, we show how kinetic studies of coupled folding and binding reactions, an important class of signaling event, are needed to determine mechanisms.     

High spatial resolution mass spectrometry imaging reveals the genetically programmed,developmental modification of the distribution of thylakoid membrane lipids among individual cells of maize leaf

Metabolism in plants is compartmentalized among different tissues, cells and subcellular organelles. Mass spectrometry imaging (MSI) with matrix‐assisted laser desorption ionization (MALDI) has recently advanced to allow for the visualization of metabolites at single‐cell resolution. Here we applied 5‐ and 10 μm high spatial resolution MALDI‐MSI to the asymmetric Kranz anatomy of Zea mays (maize) leaves to study the differential localization of two major anionic lipids in thylakoid membranes, sulfoquinovosyldiacylglycerols (SQDG) and phosphatidylglycerols (PG). The quantification and localization of SQDG and PG molecular species, among mesophyll (M) and bundle sheath (BS) cells, are compared across the leaf developmental gradient from four maize genotypes (the inbreds B73 and Mo17, and the reciprocal hybrids B73 × Mo17 and Mo17 × B73). SQDG species are uniformly distributed in both photosynthetic cell types, regardless of leaf development or genotype; however, PG shows photosynthetic cell‐specific differential localization depending on the genotype and the fatty acyl chain constituent. Overall, 16:1‐containing PGs primarily contribute to the thylakoid membranes of M cells, whereas BS chloroplasts are mostly composed of 16:0‐containing PGs. Furthermore, PG 32:0 shows genotype‐specific differences in cellular distribution, with preferential localization in BS cells for B73, but more uniform distribution between BS and M cells in Mo17. Maternal inheritance is exhibited within the hybrids, such that the localization of PG 32:0 in B73 × Mo17 is similar to the distribution in the B73 parental inbred, whereas that of Mo17 × B73 resembles the Mo17 parent. This study demonstrates the power of MALDI‐MSI to reveal unprecedented insights on metabolic outcomes in multicellular organisms at single‐cell resolution.     

Intensive research activity alters short-term seedling dynamics in a tropical forest

Researchers can have unintentional, yet significant effects on their study systems. We tested for the effects of an intensive tree census on seedling dynamics in a 50-ha permanent forest plot on Barro Colorado Island, Panama. At the community level, and for different shade-tolerance guilds, we found no significant differences in seedling recruitment or survival inside compared to controls outside the plot. However, among growth forms, canopy trees and lianas exhibited significantly lower seedling survival inside the plot. Results suggest that intense researcher activity impacts short-term vegetation dynamics, but effects do not accumulate over time.     

Impact of fly ash content and fly ash transportation distance on embodied greenhouse gas emissions and water consumption in concrete

Background, aim and scope  

Fly ash, a by-product of coal-fired power stations, is substituted for Portland cement to improve the properties of concrete and reduce the embodied greenhouse gas (GHG) emissions. Much of the world’s fly ash is currently disposed of as a waste product. While replacing some Portland cement with fly ash can reduce production costs and the embodied emissions of concrete, the relationship between fly ash content and embodied GHG emissions in concrete has not been quantified. The impact of fly ash content on embodied water is also unknown. Furthermore, it is not known whether a global trade in fly ash for use in concrete is feasible from a carbon balance perspective, or if transport over long distances would eliminate any CO₂ savings. This paper aims to quantify GHG emissions and water embodied in concrete (f′_c = 32 MPa) as a function of fly ash content and to determine the critical fly ash transportation distance, beyond which use of fly ash in concrete increases embodied GHG emissions.     

NMR assignment of prespore specific antigen—a cell surface adhesion glycoprotein from Dictyostelium discoideum

Presopore-specific antigen (PsA) is a cell surface glycoprotein of the cellular slime mould Dictyostelium discoidum implicated in cell adhesion. The ¹⁵N, ¹³C and ¹H chemical shift assignments of PsA were determined from multidimensional, multinuclear NMR experiments. Resonance assignments have been made for both the N-terminal globular domain and its attached O-glycosylated PTVT linker motif.     

A highly conserved amino-terminal region of sonic hedgehog is required for the formation of its freely diffusible multimeric form

Although members of the Hedgehog (Hh) family were initially described as morphogens, many of these early conclusions were based on experiments that used non-physiologically relevant forms of Hh. Native Hh is modified by cholesterol (HhNp) and palmitate. These hydrophobic modifications are responsible for the ability of Hh to associate with cellular membranes, a property that initially appeared inconsistent with its ability to act far from its site of synthesis. Although it is now clear that Hh family members are capable of acting directly in long-range signaling, the form of Hh capable of this activity remains controversial. We have previously provided evidence for a freely diffusible multimeric form of Sonic Hedgehog (Shh) termed s-ShhNp, which is capable of accumulating in a gradient fashion through a morphogenic field. Here, we provide further evidence that s-ShhNp is the physiologically relevant form of Shh. We show that the biological activity of freely diffusible ShhNp resides in its multimeric form and that this multimeric form is exceedingly stable, even to high concentrations of salt and detergent. Furthermore, we now validate the Shh-Shh interactions previously observed in the crystal structure of human Shh, showing that a highly conserved amino-terminal domain of Shh is important for the formation of s-ShhNp. We also conclusively show that palmitoylation is required for s-ShhNp formation. Thus, our results identify both protein-protein and protein-lipid interactions that are required for s-ShhNp formation, and provide the first structural analyses supporting the existence of Shh multimers.