Summary: A new study explores the functional evolution of the phosphoserine phosphatase (PSPH) gene across human history. The PSPH gene encodes phosphoserine phosphatase, a critical enzyme responsible for synthesizing L-serine, an amino acid essential for central nervous system development and function. Insufficient L-serine production due to pathogenic PSPH mutations leads to severe neurological deficits.
The findings demonstrate a clear functional trajectory: modern human phosphoserine phosphatase exhibits superior enzymatic function compared to diminished ancient variants, while disease-associated variants showed the weakest overall function.
Key Facts
- Functional Evolutionary Gradient: Modern human PSPH sequences demonstrate the highest level of enzymatic activity, outperforming ancient hunter-gatherer versions.
- Impaired Ancient Function: Phosphoserine phosphatase enzymes encoded by ancient hunter-gatherer genomes showed noticeably diminished functional capacity compared to their modern counterparts.
- Disease Variant Deficits: Known pathogenic, disease-associated human PSPH variants exhibited the weakest functional performance in yeast complementation assays.
- Neurological Significance: Deficiencies in L-serine synthesis caused by PSPH dysfunction are directly linked to a wide range of severe nervous system disorders.
- Methodological Advance: The study validates the power of pairing evolution-guided variant prioritization with high-throughput heterologous screening to identify subtle functional differences across human history.
Source: Wiley
Certain variants in the PSPH gene, which encodes an enzyme called phosphoserine phosphatase, prevent the body from making sufficient amounts of amino acid L-serine, leading to a range of nervous system problems.
New research in FEBS Open Bio reveals that PSPH in ancient human genomes differed functionally from modern and disease-associated versions of the gene.
Investigators found that the modern human DNA sequence of PSPH differs from sequences identified in ancient hunter-gatherers. In evolution-guided yeast complementation assays, modern-day human phosphoserine phosphatase had the greatest function, with ancient proteins showing diminished function and disease-associated variants exhibiting the weakest function.
“Our study highlights the potential of combining evolution-guided variant prioritization with scalable heterologous assays to uncover functional differences that may otherwise remain overlooked,” said co–corresponding author Alexander DeLuna, PhD, of the Center for Research and Advanced Studies (CINVESTAV), in Mexico.
Key Questions Answered:
A: L-serine is a crucial precursor for synthesized neuromodulators like D-serine and complex lipids necessary for brain development, synaptic plasticity, and myelin sheath maintenance. Insufficient L-serine production disrupts neurodevelopment and leads to microcephaly, seizures, and developmental delays.
A: The researchers used yeast complementation assays, a technique where the human PSPH gene variants are expressed inside yeast cells lacking their native equivalent. By observing how well each human variant restored normal yeast growth through L-serine synthesis, the team directly measured and compared enzymatic strength.
A: The step-wise increase in PSPH enzymatic function, from ancient hunter-gatherers to modern humans, suggests that evolutionary selective pressures favored enhanced L-serine synthesis. This biochemical optimization may have helped support the growing metabolic and neurodevelopmental demands of the modern human brain.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this genetics and evolutionary neuroscience research news
Author: Sara Henning-Stout
Source: Wiley
Contact: Sara Henning-Stout – Wiley
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Evolution-guided yeast complementation reveals functional differences in human PSPH variants” by Mauricio Campa-Álvarez, Diana Ascencio, Miguel Vallebueno-Estrada, Eduardo González-Orozco, Christian Eduardo Martínez-Guerrero, Rafael Montiel, Alexander DeLuna. FEBS Open Bio
DOI:10.1002/2211-5463.70308
Abstract
Evolution-guided yeast complementation reveals functional differences in human PSPH variants
Deciphering how human genetic variants affect conserved metabolic enzymes is essential for understanding their evolutionary and clinical significance.
Here, we combine sequence analyses of temporally stratified human genomes with a quantitative Saccharomyces cerevisiae complementation assay in a strain lacking SER2, the yeast gene required for the final step of L-serine biosynthesis, to examine functional differences among human phosphoserine phosphatase (PSPH) variants.
Population-genomic comparisons between ancient hunter-gatherers and present-day humans identified two PSPH exons with elevated differences in nucleotide diversity, guiding the selection of two ancient-genome-prioritized variants (R27S and Q83H) for functional testing.
To place their effects in functional context, we expressed each variant individually and compared complementation with the modern PSPH allele and two disease-associated alleles (D32N and A35T) across multiple environmental conditions. Human PSPH enhanced growth of the SER2 deletion mutant and revealed reproducible quantitative differences among alleles.
The modern allele generally conferred the strongest complementation, while the ancient genome variants supported measurable but more condition-dependent rescue, and the disease-associated alleles showed the weakest complementation. These differences were broadly consistent across conditions, while specific environmental perturbations revealed context-dependent shifts in effect size.
Together, our results establish a scalable framework that links evolutionary genomics with experimental functional assays to identify and evaluate human metabolic enzyme variants with measurable in vivo effects.
