Frog foams and natural protein surfactants

Foams and surfactants are relatively rare in biology because of their potential to harm cell membranes and other delicate tissues. However, in recent work we have identified and characterized a number of natural surfactant proteins found in the foam nests of tropical frogs and other unusual sources. These proteins, and their associated foams, are relatively stable and bio-compatible, but with intriguing molecular structures that reveal a new class of surfactant activity. Here we review the structures and functional mechanisms of some of these proteins as revealed by experiments involving a range of biophysical and biochemical techniques, with additional mechanistic support coming from more recent site-directed mutagenesis studies

Aqueous solubilization of C60 fullerene by natural protein surfactants, latherin and ranaspumin-2

C60 fullerene is not soluble in water and dispersion usually requires organic solvents, sonication or vigorous mechanical mixing. However, we show here that mixing of pristine C60 in water with natural surfactant proteins latherin and ranaspumin-2 (Rsn-2) at low concentrations yields stable aqueous dispersions with spectroscopic properties similar to those previously obtained by more vigorous methods. Particle sizes are significantly smaller than those achieved by mechanical dispersion alone, and concentrations are compatible with clusters approximating 1:1 protein:C60 stoichiometry. These proteins can also be adsorbed onto more intractable carbon nanotubes. This promises to be a convenient way to interface a range of hydrophobic nanoparticles and related materials with biological macromolecules, with potential to exploit the versatility of recombinant protein engineering in the development of nano-bio interface devices. It also has potential consequences for toxicological aspects of these and similar nanoparticles

Resonance assignments for latherin, a natural surfactant protein from horse sweat

Latherin is an intrinsically surfactant protein of ~23 kDa found in the sweat and saliva of horses. Its function is probably to enhance the translocation of sweat water from the skin to the surface of the pelt for evaporative cooling. Its role in saliva may be to enhance the wetting, softening and maceration of the dry, fibrous food for which equines are adapted. Latherin is unusual in its relatively high content of aliphatic amino acids (~25 % leucines) that might contribute to its surfactant properties. Latherin is related to the palate, lung, and nasal epithelium carcinoma-associated proteins (PLUNCs) of mammals, at least one of which is now known to exhibit similar surfactant activity to latherin. No structures of any PLUNC protein are currently available. 15N,13C-labelled recombinant latherin was produced in Escherichia coli, and essentially all of the resonances were assigned despite the signal overlap due to the preponderance of leucines. The most notable exceptions include a number of residues located in an apparently dynamic loop region between residues 145 and 154. The assignments have been deposited with BMRB accession number 19067

Anti-Parallel β-Hairpin Structure in Soluble Aβ Oligomers of Aβ40-Dutch and Aβ40-Iowa

The amyloid-β (Aβ) peptides are associated with two prominent diseases in the brain, Alzheimer’s disease (AD) and cerebral amyloid angiopathy (CAA). Aβ42 is the dominant component of cored parenchymal plaques associated with AD, while Aβ40 is the predominant component of vascular amyloid associated with CAA. There are familial CAA mutations at positions Glu22 and Asp23 that lead to aggressive Aβ aggregation, drive vascular amyloid deposition and result in degradation of vascular membranes. In this study, we compared the transition of the monomeric Aβ40-WT peptide into soluble oligomers and fibrils with the corresponding transitions of the Aβ40-Dutch (E22Q), Aβ40-Iowa (D23N) and Aβ40-Dutch, Iowa (E22Q, D23N) mutants. FTIR measurements show that in a fashion similar to Aβ40-WT, the familial CAA mutants form transient intermediates with anti-parallel β-structure. This structure appears before the formation of cross-β-sheet fibrils as determined by thioflavin T fluorescence and circular dichroism spectroscopy and occurs when AFM images reveal the presence of soluble oligomers and protofibrils. Although the anti-parallel β-hairpin is a common intermediate on the pathway to Aβ fibrils for the four peptides studied, the rate of conversion to cross-β-sheet fibril structure differs for each

The structure of latherin, a surfactant allergen protein from horse sweat and saliva

Latherin is a highly surface-active allergen protein found in the sweat and saliva of horses and other equids. Its surfactant activity is intrinsic to the protein in its native form, and is manifest without associated lipids or glycosylation. Latherin probably functions as a wetting agent in evaporative cooling in horses, but it may also assist in mastication of fibrous food as well as inhibition of microbial biofilms. It is a member of the PLUNC family of proteins abundant in the oral cavity and saliva of mammals, one of which has also been shown to be a surfactant and capable of disrupting microbial biofilms. How these proteins work as surfactants while remaining soluble and cell membrane-compatible is not known. Nor have their structures previously been reported. We have used protein nuclear magnetic resonance spectroscopy to determine the conformation and dynamics of latherin in aqueous solution. The protein is a monomer in solution with a slightly curved cylindrical structure exhibiting a ‘super-roll’ motif comprising a four-stranded anti-parallel β-sheet and two opposing α-helices which twist along the long axis of the cylinder. One end of the molecule has prominent, flexible loops that contain a number of apolar amino acid side chains. This, together with previous biophysical observations, leads us to a plausible mechanism for surfactant activity in which the molecule is first localized to the non-polar interface via these loops, and then unfolds and flattens to expose its hydrophobic interior to the air or non-polar surface. Intrinsically surface-active proteins are relatively rare in nature, and this is the first structure of such a protein from mammals to be reported. Both its conformation and proposed method of action are different from other, non-mammalian surfactant proteins investigated so far

LLC and Partnership Transfer Restrictions Excluded From UCC Article 9 Overrides

The organizational law of limited liability companies (LLCs) and partnerships has always fundamentally embraced an idea known as the “pick-your-partner principle,” under which transfers of a member’s or partner’s ownership interest are restricted by statute, and those restrictions may be tightened or loosened by agreement. In recent years the pick-your-partner principle has interacted in complex and not always practical ways with Article 9 of the Uniform Commercial Code (UCC). Since 2001, UCC §§ 9-406 and 9-408 have overridden a broad range of statutory and agreement-based anti-assignment provisions, subject to complex exceptions that have tended to protect the pick-your-partner principle in many significant respects, while also proving analytically very difficult to handle. Recently, however, in an important step forward, Article 9’s overrides of anti-assignment provisions have been amended to make them simply inapplicable to LLC and partnership interests. One hopes that these amendments to Article 9’s overrides (hereinafter the “2018 amendments” because they were approved last year) will soon be enacted by the states, but in the meantime, the current overrides will remain on the books in various jurisdictions with all of their existing complexities. Accordingly, this article focuses not only on the 2018 amendments, but also on an analysis of the overrides as they now stand, as applied to LLC and partnership interests. The amendments themselves are quite simple, but the article discusses them only after analyzing the overrides because the amendments are more easily understood against that background

Nine challenges in modelling the emergence of novel pathogens.

Studying the emergence of novel infectious agents involves many processes spanning host species, spatial scales, and scientific disciplines. Mathematical models play an essential role in combining insights from these investigations and drawing robust inferences from field and experimental data. We describe nine challenges in modelling the emergence of novel pathogens, emphasizing the interface between models and data.We acknowledge support from the Research and Policy for Infectious Disease Dynamics (RAPIDD) programme of the Science and Technology Directory, Department of Homeland Security, and Fogarty International Center, National Institutes of Health. JLS was also supported by the National Science Foundation (EF-0928987 and OCE-1335657) and the De Logi Chair in Biological Sciences. SF was supported by a UK Medical Research Council Career Development Award in Biostatistics. SR was supported by: Wellcome Trust Project Award 093488/Z/10/Z; R01 TW008246-01 from Fogarty International Centre; and The Medical Research Council (UK, Project Grant MR/J008761/1). JLNW was also supported by the Alborada Trust and the European Union FP7 project ANTIGONE (contract number 278976).This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.epidem.2014.09.00

Structural and functional roles of small group-conserved amino acids present on helix-H7 in the β2-adrenergic receptor

AbstractSequence analysis of the class A G protein-coupled receptors (GPCRs) reveals that most of the highly conserved sites are located in the transmembrane helices. A second level of conservation exists involving those residues that are conserved as a group characterized by small and/or weakly polar side chains (Ala, Gly, Ser, Cys, Thr). These positions can have group conservation levels of up to 99% across the class A GPCRs and have been implicated in mediating helix–helix interactions in membrane proteins. We have previously shown that mutation of group-conserved residues present on transmembrane helices H2–H4 in the β2-adrenergic receptor (β2-AR) can influence both receptor expression and function. We now target the group-conserved sites, Gly3157.42 and Ser3197.46, on H7 for structure-function analysis. Replacing Ser3197.46 with smaller amino acids (Ala or Gly) did not influence the ability of the mutant receptors to bind to the antagonist dihydroalprenolol (DHA) but resulted in ~15–20% agonist-independent activity. Replacement of Ser3197.46 with the larger amino acid leucine lowered the expression of the S319L mutant and its ability to bind DHA. Both the G315A and G315S mutants also exhibited agonist-independent signaling, while the G315L mutant did not show specific binding to DHA. These data indicate that Gly3157.42 and Ser3197.46 are stabilizing β2-AR in an inactive conformation. We discuss our results in the context of van der Waals interactions of Gly3157.42 with Trp2866.48 and hydrogen bonding interactions of Ser3197.46 with amino acids on H1–H2–H7 and with structural water