Prediction of the secondary structure of proteins from their amino acid sequence.

Glycobiology: Toward Understanding the Function of Sugars.

https://science.sciencemag.org/content/sci/177/4053/949.full.pdf

Lectins: cell-agglutinating and sugar-specific proteins.

Simple and complex carbohydrates (glycans) have long been known to play major metabolic, structural and physical roles in biological systems. Targeted microbial binding to host glycans has also been studied for decades. But such biological roles can only explain some of the remarkable complexity and organismal diversity of glycans in nature. Reviewing the subject about two decades ago, one could find very few clear-cut instances of glycan-recognition-specific biological roles of glycans that were of intrinsic value to the organism expressing them. In striking contrast there is now a profusion of examples, such that this updated review cannot be comprehensive. Instead, a historical overview is presented, broad principles outlined and a few examples cited, representing diverse types of roles, mediated by various glycan classes, in different evolutionary lineages. What remains unchanged is the fact that while all theories regarding biological roles of glycans are supported by compelling evidence, exceptions to each can be found. In retrospect, this is not surprising. Complex and diverse glycans appear to be ubiquitous to all cells in nature, and essential to all life forms. Thus, >3 billion years of evolution consistently generated organisms that use these molecules for many key biological roles, even while sometimes coopting them for minor functions. In this respect, glycans are no different from other major macromolecular building blocks of life (nucleic acids, proteins and lipids), simply more rapidly evolving and complex. It is time for the diverse functional roles of glycans to be fully incorporated into the mainstream of biological sciences.

/pdf/biological-roles-of-glycans-zowb8sw07y.pdf

Biological Roles of Glycans

Publisher Summary Lectins play an important role in the development of immunology. Lectins also find application in serological laboratories for typing blood and determining secretor status, separating leucocytes from erythrocytes, and agglutinating cells from blood in the preparation of plasma. They serve as reagents for the detection, isolation, and characterization of carbohydrate-containing macromolecules, including blood-group antigens. In their interaction with saccharides, lectins serve as models for carbohydrate-specific antibodies, with the important advantage to purify lectins in gram quantities. Lectins are classified according to their carbohydrate-binding specificity that includes D-mannose(D-glucose)-binding lectins and 2-acetamido-2-deoxy-D-glucose-binding lectins. The chapter considers only those lectins that have been purified to homogeneity, and studied with regard to their biophysical, biochemical, and carbohydrate-binding specificity. The chapter also describes the cell-binding and biological properties of lectins. The chapter concludes with the description of several glycopeptide structures showing the carbohydrate-binding loci with which various lectins interact.

The lectins : carbohydrate-binding proteins of plants and animals

Galectins: a family of animal beta-galactoside-binding lectins.

Intracellular functions of galectins

AprilTags and other passive fiducial markers require specialized algorithms to detect markers among other features in a natural scene. The vision processing steps generally dominate the computation time of a tag detection pipeline, so even small improvements in marker detection can translate to a faster tag detection system. We incorporated lessons learned from implementing and supporting the AprilTag system into this improved system. This work describes AprilTag 2, a completely redesigned tag detector that improves robustness and efficiency compared to the original AprilTag system. The tag coding scheme is unchanged, retaining the same robustness to false positives inherent to the coding system. The new detector improves performance with higher detection rates, fewer false positives, and lower computational time. Improved performance on small images allows the use of decimated input images, resulting in dramatic gains in detection speed.

AprilTag 2: Efficient and robust fiducial detection

The tentative amino-acid sequence and three-dimensional structure of the lectin concanavalin A have been determined. The amino-acid sequence, which was determined chemically, contains 238 residues. The sequences of three short stretches were assigned on the basis of x-ray crystallographic data. Interpretation of an electron density map at 2-A resolution indicates that the predominant structural element is extended polypeptide chain arranged in two anti-parallel pleated sheets or β-structures. Residues not included in the β-structures are arranged in regions of random coil. One of the pleated sheets contributes extensively to the interactions among the monomers to form both dimers and tetramers. The positions at which Mn2+, Ca2+, and saccharide are bound to the protein, and the point of cleavage for the formation of the naturally occurring fragments A1 and A2, have been tentatively assigned. Both metal-binding sites are at least 20-A removed from the position at which saccharides are bound. The saccharide-binding site is a deep pocket of approximately 6A × 7.5A × 18A, the inner portion of which is occupied by hydrophobic residues.

https://www.pnas.org/content/pnas/69/9/2580.full.pdf

The Covalent and Three-Dimensional Structure of Concanavalin A

An analysis of the inhibition by concanavalin A of the mobility of lymphocyte surface receptors is used to construct an hypothesis on membrane receptor-cytoplasmic interactions. It is proposed that binding of multivalent lectins alters the interaction of an assembly of colchicine-binding proteins with lectin receptors and other receptors, and reciprocally that the state of the colchicine-binding assembly alters the mobility and distribution of surface receptors on the cell membrane. Observations of the effect of colchicine and related drugs on the inhibition of receptor mobility by concanavalin A lend support to this hypothesis. The proposed model has several implications for studies of the initial events of mitogenesis in lymphocytes as well as for cell-cell interactions in general.

https://www.pnas.org/content/pnas/70/5/1442.full.pdf

John L. Wang

Papers

Galectins: a family of animal beta-galactoside-binding lectins.

Intracellular functions of galectins

AprilTag 2: Efficient and robust fiducial detection

The Covalent and Three-Dimensional Structure of Concanavalin A

Receptor mobility and receptor-cytoplasmic interactions in lymphocytes.