Biallelic variants in the SLC13A1 sulfate transporter gene cause hyposulfatemia with a mild spondylo-epi-metaphyseal dysplasia

Analytical methods for quantitating sulfate in plasma and serum

Circulating sulfate needs to be maintained at sufficiently high levels for healthy growth and development. Animal studies have shown the adverse physiological consequences of low circulating sulfate level on the skeletal, neurological and reproductive systems. However, sulfate is not routinely measured in clinical investigations, despite the importance of sulfate being documented over the past several decades. Several methods have been developed for measuring serum and plasma sulfate level in animals and humans, including a range of barium sulfate precipitation techniques that have been a major focus of sulfate analytics since the 1960s. Evaluation of an ion chromatography method demonstrated its utility for investigation of sulfate levels in human health. More recently, liquid chromatography-tandem mass spectrometry has been used to show hyposulfatemia in a human case of mild skeletal dysplasia. This article provides an overview of analytical methods for measuring sulfate in serum and plasma, highlighting the strengths and limitations of each method.

Complementary structures of the yeast phosphate transporter Pho90 provide insights into its transport mechanism

Phosphate homeostasis is essential for all living organisms. Low-affinity phosphate transporters are involved in phosphate import and regulation in a range of eukaryotic organisms. We have determined the structures of the Saccharomyces cerevisiae phosphate importer Pho90 by electron cryomicroscopy in two complementary states at 2.3 and 3.1 Å resolution. The symmetrical, outward-open structure in the presence of phosphate indicates bound substrate ions in the binding pocket. In the absence of phosphate, Pho90 assumes an asymmetric structure with one monomer facing inward and one monomer facing outward, providing insights into the transport mechanism. The Pho90 transport domain binds phosphate ions on one side of the membrane, then flips to the other side where the substrate is released. Together with functional experiments, these complementary structures illustrate the transport mechanism of eukaryotic low-affinity phosphate transporters.

Sulfate: a neglected (but potentially highly relevant) anion

Sulfate is an important anion as sulfonation is essential in modulation of several compounds, such as exogens, polysaccharide chains of proteoglycans, cholesterol or cholesterol derivatives and tyrosine residues of several proteins. Sulfonation requires the presence of both the sulfate donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) and a sulfotransferase. Genetic disorders affecting sulfonation, associated with skeletal abnormalities, impaired neurological development and endocrinopathies, demonstrate the importance of sulfate. Yet sulfate is not measured in clinical practice. This review addresses sulfate metabolism and consequences of sulfonation defects, how to measure sulfate and why we should measure sulfate more often.

Sulfur-Element containing metabolic pathways in human health and crosstalk with the microbiome

In humans, methionine derived from dietary proteins is necessary for cellular homeostasis and regeneration of sulfur containing pathways, which produce inorganic sulfur species (ISS) along with essential organic sulfur compounds (OSC). In recent years, inorganic sulfur species have gained attention as key players in the crosstalk of human health and the gut microbiome. Endogenously, ISS includes hydrogen sulfide (H2S), sulfite (SO32-), thiosulfate (S2O32-), and sulfate (SO42-), which are produced by enzymes in the transsulfuration and sulfur oxidation pathways. Additionally, sulfate-reducing bacteria (SRB) in the gut lumen are notable H2S producers which can contribute to the ISS pools of the human host. In this review, we will focus on the systemic effects of sulfur in biological pathways, describe the contrasting mechanisms of sulfurylation versus phosphorylation on the hydroxyl of serine/threonine and tyrosine residues of proteins in post-translational modifications, and the role of the gut microbiome in human sulfur metabolism.