Determinants of tyrosylprotein sulfation coding and substrate specificity of tyrosylprotein sulfotransferases in metazoans

The origins and developments of sulfation-prone tyrosine-rich and acidic N- and C-terminal extensions of class ll and lll small leucine-rich repeat proteins shed light on connective tissue evolution in vertebrates

Background

Small leucine-rich repeat protein (SLRP) family members contain conserved leucine-rich repeat motifs flanked by highly variable N- and C-terminal regions. Most class II and III SLRPs have tyrosine-rich N-terminal regions and some of these are sulfated. However, the evolutionary origin and conservation of the tyrosine-rich and acidic terminal regions remain undetermined. In this study, we present the most comprehensive multiple sequence alignment (MSA) analyses of all eight class II and III SLRPs to date. Based on the level of conservation of tyrosine residues and adjacent sequences, we predict which tyrosine residues are most likely to be sulfated in the terminal regions of human class II and III SLRPs.

Results

Using this novel approach, we predict a total of 22 tyrosine sulfation sites in human SLRPs, of which only 8 sites had been experimentally identified in mammals. Our analyses suggest that sulfation-prone, tyrosine-rich and acidic terminal regions of the class II and III SLRPs emerged via convergent evolution at different stages of vertebrate evolution, coinciding with significant evolutionary events including the development of endochondral bones and articular cartilage, the aquatic to terrestrial transition, and the formation of an amnion.

Conclusions

Our study suggests that selective pressures due to changes in life conditions led to the formation of sulfotyrosine-rich and acidic terminal regions. We believe the independent emergence and evolution of sulfotyrosine-rich and acidic N- and C-terminal regions have provided each class II and III SLRP member with novel vital functions required to develop new specialized extracellular matrices and tissues in vertebrate species.

Host-Receptor Post-Translational Modifications Refine Staphylococcal Leukocidin Cytotoxicity

Staphylococcal bi-component pore-forming toxins, also known as leukocidins, target and lyse human phagocytes in a receptor-dependent manner. S-components of the leukocidins Panton-Valentine leukocidin (PVL), γ-haemolysin AB (HlgAB) and CB (HlgCB), and leukocidin ED (LukED) specifically employ receptors that belong to the class of G-protein coupled receptors (GPCRs). Although these receptors share a common structural architecture, little is known about the conserved characteristics of the interaction between leukocidins and GPCRs. In this study, we investigated host cellular pathways contributing to susceptibility towards S. aureus leukocidin cytotoxicity. We performed a genome-wide CRISPR/Cas9 library screen for toxin-resistance in U937 cells sensitized to leukocidins by ectopic expression of different GPCRs. Our screen identifies post-translational modification (PTM) pathways involved in the sulfation and sialylation of the leukocidin-receptors. Subsequent validation experiments show differences in the impact of PTM moieties on leukocidin toxicity, highlighting an additional layer of refinement and divergence in the staphylococcal host-pathogen interface. Leukocidin receptors may serve as targets for anti-staphylococcal interventions and understanding toxin-receptor interactions will facilitate the development of innovative therapeutics. Variations in the genes encoding PTM pathways could provide insight into observed differences in susceptibility of humans to infections with S. aureus.

Sulfation pathways from red to green

Sulfur is present in the amino acids cysteine and methionine and in a large range of essential coenzymes and cofactors and is therefore essential for all organisms. It is also a constituent of sulfate esters in proteins, carbohydrates, and numerous cellular metabolites. The sulfation and desulfation reactions modifying a variety of different substrates are commonly known as sulfation pathways. Although relatively little is known about the function of most sulfated metabolites, the synthesis of activated sulfate used in sulfation pathways is essential in both animal and plant kingdoms. In humans, mutations in the genes encoding the sulfation pathway enzymes underlie a number of developmental aberrations, and in flies and worms, their loss-of-function is fatal. In plants, a lower capacity for synthesizing activated sulfate for sulfation reactions results in dwarfism, and a complete loss of activated sulfate synthesis is also lethal. Here, we review the similarities and differences in sulfation pathways and associated processes in animals and plants, and we point out how they diverge from bacteria and yeast. We highlight the open questions concerning localization, regulation, and importance of sulfation pathways in both kingdoms and the ways in which findings from these "red" and "green" experimental systems may help reciprocally address questions specific to each of the systems.

Characterization of a Sulfated Anti-HIV Antibody Using an Expanded Genetic Code

Tyrosine sulfation is a crucial post-translational modification for certain antibodies that neutralize HIV. One of the most neutralizing sulfated anti-HIV antibodies, E51, contains a region in its V_HCDR3 loop with five tyrosine (Tyr) residues, which are hypothesized to be partially or fully sulfated to bind to HIV's gp120 coat protein. However, the gp120-binding contribution of each sulfate or more complex sulfation patterns is unknown. In addition, natural sulfation of Tyr-rich loops usually yields a mixture of multiply sulfated products, complicating attempts to dissect the function of individual E51 sulfoforms with unique sulfation patterns. Here, we use an upgraded expanded genetic code for sulfotyrosine (sY) to express homogeneous E51 sulfoforms containing up to five sulfates. Through characterization of the 32 possible sulfoforms of E51, we show that only a subset of E51 sulfoforms with two, three, or four sYs bind to gp120 with potency similar to that of post-translationally sulfated E51, which we find is a mixture of sulfoforms. We show that sulfation of Tyr100i is necessary for gp120 binding whereas sulfation of Tyr100n is detrimental to binding. These results reveal that gp120 binding by E51 requires very specific sulfation patterns and should aid in the further design of sulfated E51-based peptides and immunoadhesins against HIV.