Regulation of integrin affinity (activation) is essential for metazoan development and for many pathological processes. Binding of the talin phosphotyrosine-binding (PTB) domain to integrin beta subunit cytoplasmic domains (tails) causes activation, whereas numerous other PTB-domain-containing proteins bind integrins without activating them. Here we define the structure of a complex between talin and the membrane-proximal integrin beta3 cytoplasmic domain and identify specific contacts between talin and the integrin tail required for activation. We used structure-based mutagenesis to engineer talin and beta3 variants that interact with comparable affinity to the wild-type proteins but inhibit integrin activation by competing with endogenous talin. These results reveal the structural basis of talin's unique ability to activate integrins, identify an interaction that could aid in the design of therapeutics to block integrin activation, and enable engineering of cells with defects in the activation of multiple classes of integrins.

Staphylococcus aureus and Streptococcus pyogenes, two important human pathogens, target host fibronectin (Fn) in their adhesion to and invasion of host cells. Fibronectin-binding proteins (FnBPs), anchored in the bacterial cell wall, have multiple Fn-binding repeats in an unfolded region of the protein. The bacterium-binding site in the amino-terminal domain (1-5F1) of Fn contains five sequential Fn type 1 (F1) modules. Here we show the structure of a streptococcal (S. dysgalactiae) FnBP peptide (B3) in complex with the module pair 1F12F1. This identifies 1F1- and 2F1-binding motifs in B3 that form additional antiparallel beta-strands on sequential F1 modules-the first example of a tandem beta-zipper. Sequence analyses of larger regions of FnBPs from S. pyogenes and S. aureus reveal a repeating pattern of F1-binding motifs that match the pattern of F1 modules in 1-5F1 of Fn. In the process of Fn-mediated invasion of host cells, therefore, the bacterial proteins seem to exploit the modular structure of Fn by forming extended tandem beta-zippers. This work is a vital step forward in explaining the full mechanism of the integrin-dependent FnBP-mediated invasion of host cells.

Adhesive interactions involving CD44, the cell surface receptor for hyaluronan, underlie fundamental processes such as inflammatory leukocyte homing and tumor metastasis. Regulation of such events is critical and appears to be effected by changes in CD44 N-glycosylation that switch the receptor "on" or "off" under appropriate circumstances. How altered glycosylation influences binding of hyaluronan to the lectin-like Link module in CD44 is unclear, although evidence suggests additional flanking sequences peculiar to CD44 may be involved. Here we show using X-ray crystallography and NMR spectroscopy that these sequences form a lobular extension to the Link module, creating an enlarged HA binding domain and a formerly unidentified protein fold. Moreover, the disposition of key N-glycosylation sites reveals how specific sugar chains could alter both the affinity and avidity of CD44 HA binding. Our results provide the necessary structural framework for understanding the diverse functions of CD44 and developing novel therapeutic strategies.

The solution structure of the Link module from human TSG-6, a hyaladherin with important roles in inflammation and ovulation, has been determined in both its free and hyaluronan-bound conformations. This reveals a well defined hyaluronan-binding groove on one face of the Link module that is closed in the absence of ligand. The groove is lined with amino acids that have been implicated in mediating the interaction with hyaluronan, including two tyrosine residues that appear to form essential intermolecular hydrogen bonds and two basic residues capable of supporting ionic interactions. This is the first structure of a non-enzymic hyaladherin in its active state, and identifies a ligand-induced conformational change that is likely to be conserved across the Link module superfamily. NMR and isothermal titration calorimetry experiments with defined oligosaccharides have allowed us to infer the minimum length of hyaluronan that can be accommodated within the binding site and its polarity in the groove; these data have been used to generate a model of the complex formed between the Link module and a hyaluronan octasaccharide.Hyaluronan (HA), 1 a high molecular weight polysaccharide with a central role in extracellular matrix organization and cell adhesion in mammals (1), is essential to a wide range of normal physiological processes including development, immunology, and reproduction (2-4). Alterations in the metabolism and localization of this molecule underlie the progression of many diseases, for instance arthritis, pulmonary/vascular disorders, and cancer (5, 6). These diverse biological activities may seem surprising for a linear polymer composed entirely of a repeating disaccharide (i.e. -glucuronic acid-␤Ϫ1,3-N-acetylglucosamine-␤Ϫ1,4-; up to 10 7 Da) that, unlike other glycosaminoglycans, is neither attached to a core protein nor sulfated. This functional complexity is thought to arise from the interaction of HA with a large number of specific HA-binding proteins (7), which can form structurally diverse complexes (see Ref. 8). The majority of these "hyaladherins" belong to a superfamily of proteins that share a common ϳ100 amino acid domain, termed a Link module, that mediates the interaction with HA.Previously we have determined the solution structure of the Link module from human TSG-6 (the protein product of the tumor necrosis factor-stimulated gene-6 (9)), thereby defining the consensus fold for this superfamily (10). In TSG-6, a 35-kDa secreted protein composed mainly of contiguous Link and CUB modules, the Link module is sufficient to mediate a high affinity interaction with HA (10, 11); this has been termed a "type A" HA-binding domain (7). The HA receptor CD44, which has an important role in mediating lymphocyte migration, however, requires N-and C-terminal extensions to its Link module for correct folding and functional activity of its type B interaction domain. Most other members of the superfamily, such as link proteins and chondroitin-sulfate proteoglycans (critical for extracellular matrix organiza...

This study presents a comprehensive process, economic, environmental, and socioeconomic analysis of the enzymatic recycling of poly(ethylene terephthalate), which is the most widely used synthetic polyester. The analyses predict that PET deconstruction using enzymes can achieve cost parity with terephthalic acid manufacturing as well as substantial reductions in both supply chain energy use and greenhouse gas emissions relative to virgin polyester manufacturing. This study also highlights key research areas for further impactful development of biocatalysis-enabled plastics recycling.