Illuminating the impact of N-terminal acetylation: from protein to physiology

Identification of Histone and N-Terminal Acetyltransferases Required for Reproduction and Embryonic Development of Yellow Fever Mosquito, Aedes aegypti

Histone acetylation levels maintained by histone acetyltransferases (HATs) and histone deacetylases play important roles in maintaining local chromatin accessibility and expression of genes that regulate many biological processes, including development and reproduction. N-terminal acetylation of proteins catalyzed by N-terminal acetyltransferases (NATs) also regulates gene expression. We identified 25 HATs/NATs genes in the yellow fever mosquito, Aedes aegypti, and investigated their function in female reproduction using RNA interference (RNAi). Among the HATs/NATs studied, the knockdown of AANAT1 (Arylamine N-acetyltransferase), NAA40 (N-alpha-acetyltransferase 40), NAA80 (N-alpha-acetyltransferase 80), KAT7 (Histone lysine acetyltransferase 7), ACNAT (Acyl-CoA N-acyltransferase), and MCM3AP (Minichromosome maintenance complex component 3 associated protein) significantly reduced egg laying and caused severe problems in oocyte development compared to that in control insects injected with dsGFP. Gene expression analysis using RT-qPCR revealed that vitellogenin and its receptor genes are downregulated in mosquitoes injected with dsAANAT1, dsNAA40, dsNAA80, dsKAT7, dsACNAT, and dsMCM3AP compared to that in control animals. Also, the knockdown of HATs/NATs genes ATAT1 (Alpha-tubulin N-acetyltransferase 1), AANAT1, TAFIID (Transcription initiation factor TFIID subunit 1), HATB (Histone acetyltransferase type B) and NAT9 (N-acetyltransferase 9) decreased more than 50% egg hatch by blocking embryonic development. These results suggest that the acetylation of proteins, especially histones mediated by NATs and HATs, plays an important role in regulating female reproduction and embryonic development of Ae. aegypti.

Understanding peptide hormones: from precursor proteins to bioactive molecules

Peptide hormones are fundamental regulators of biological processes involved in homeostasis regulation and are often dysregulated in endocrine diseases. Despite their biological significance and established therapeutic potential, there is still a gap in our knowledge of their processing and post-translational modifications, as well as in the technologies for their discovery and detection. In this review, we cover insights into the peptidome landscape, including the proteolytic processing and post-translational modifications of peptide hormones. Understanding the full landscape of peptide hormones and their modifications could provide insights into leveraging proteolytic mechanisms to identify novel peptides with therapeutic potential. Therefore, we also discuss the need for future research aiming at better predicting, detecting, and characterizing new peptides with biological activities.

Decoding a novel non-enzymatic protein acetylation mechanism in sperm that is essential for fertilizing potential

BACKGROUND

Protein acetylation has emerged as essential for sperm function, attracting considerable attention recently. Acetylation, typically mediated by lysine acetyltransferases, involves attaching an acetyl group from acetyl-coenzyme A to lysine residues in proteins. Under alkaline conditions, however, acetylation can occur with minimal enzymatic involvement, primarily due to an elevated pH. As sperm migrate towards the ampulla, they experience increasing intracellular pH (pHi) while undergoing two crucial processes for fertilization: capacitation and the acrosome reaction (AR). Whereas the involvement of acetylating enzymes in these events has been partially investigated, the potential for non-enzymatic acetylation driven by the pHi alkalinization remains unknown.

RESULTS

This study examined protein acetylation (acLys) levels in sperm incubated under capacitating conditions at pH 7.2 and pH 9.0, the latter condition potentially promoting non-enzymatic acetylation. To more precisely investigate the occurrence of non-enzymatic acetylation events, acetyltransferase activity was selectively attenuated using a specific cocktail of inhibitors. The functional implications of these conditions were assessed by examining key fertilization-related sperm attributes, including motility during capacitation and the ability to initiate the AR. Results demonstrated that alkaline conditions elevated basal acLys levels even with reduced acetyltransferase activity (P < 0.05), indicative of non-enzymatic acetylation. α-tubulin, particularly in the midpiece of the sperm flagellum, was identified as a specific target of this modification, correlating with diminished motility during capacitation. Following the AR, acLys levels in the head and midpiece decreased (P < 0.05) under conditions promoting non-enzymatic acetylation, accompanied by reductions in intracellular and acrosomal pH. In contrast, acLys levels and pH in the sperm head incubated under standard capacitating conditions (pH 7.2) remained stable. Sperm exposed to conditions conducive to non-enzymatic acetylation exhibited an impaired ability to trigger the AR (P < 0.05) compared to those maintained at pH 7.2. Notably, diminished acetylase activity emerged as a key factor impairing the maintenance of intracellular and acrosomal pH levels attained during capacitation, even under a pH of 9.0.

CONCLUSION

This study provides novel evidence for the occurrence of non-enzymatic acetylation in sperm, linked to the modulation of α-tubulin acetylation levels and motility during capacitation. Additionally, it suggests that acetyltransferase activity may play a crucial role in regulating intracellular and acrosomal pH levels in capacitated sperm, facilitating the AR.

OsHYPK/NatA-mediated N-terminal acetylation regulates the homeostasis of NLR immune protein to fine-tune rice immune responses and growth

Keeping nucleotide-binding leucine-rich repeat (NLR) protein at appropriate levels is critical for plant survival. Huntingtin Yeast Partner K (OsHYPK) was previously identified as a positive regulator of N-terminal acetyltransferase A (NatA) activity in rice. Here, we find that oshypk shows enhanced resistance to Magnaporthe oryzae (M. oryzae). Through screening for suppressors of oshypk (soh), we identify suppressor soh74, which contains a mutation in RESISTANCE TO P. SYRINGAE PV MACULICOLA1 (RPM1)-like NLR protein (RPM1-L1) and exhibits compromised resistance to M. oryzae. Mechanistically, declined N-terminal acetylation (NTA) degree in oshypk leads to protein accumulation of RPM1-L1, contributing to enhanced disease resistance. To restrict RPM1-L1 accumulation, OsHYPK is expressed at high levels under normal conditions. However, pathogen infection reduces OsHYPK level to release the inhibition on RPM1-L1, leading to immune activation. This study reveals a vital pathway in which OsHYPK/NatA-mediated NTA rapidly fine-tunes NLR-mediated immune response.

DCHS1 Modulates Forebrain Proportions in Modern Humans via a Glycosylation Change

Comparative anatomical studies of primates and extinct hominins, including Neanderthals, show that the modern human brain is characterised by a disproportionately enlarged neocortex relative to the striatum. To explore the molecular basis of this difference, we screened for missense mutations that are unique to modern humans and occur at high frequency and that alter post-translational sites. One such mutation was identified in DCHS1, a protocadherin family gene, and it was found to disrupt an N-glycosylation site in modern humans. Using CRISPR/Cas9-editing we introduced into human-induced pluripotent stem cells (hiPSCs) this ancestral DCHS1 variant present in Neanderthals and other primates, representing the ancestral state before the modern human-specific substitution. Leveraging hiPSCs-derived neural organoids, we observed an expansion of striatal progenitors at the expense of the neocortex, mirroring the anatomical distribution seen in non-human primates. We further identify the ephrin receptor EPHA4 as a binding partner of DCHS1 and show that modern human-specific alterations in DCHS1 modulate EPHA4-ephrin signalling, contributing to a gradual shift in the neocortex-to-striatum ratio - a hallmark of brain organisation in our species.

The nascent polypeptide-associated complex (NAC) as regulatory hub on ribosomes

The correct synthesis of new proteins is essential for maintaining a functional proteome and cell viability. This process is tightly regulated, with ribosomes and associated protein biogenesis factors ensuring proper protein production, modification, and targeting. In eukaryotes, the conserved nascent polypeptide-associated complex (NAC) plays a central role in coordinating early protein processing by regulating the ribosome access of multiple protein biogenesis factors. NAC recruits modifying enzymes to the ribosomal exit site to process the N-terminus of nascent proteins and directs secretory proteins into the SRP-mediated targeting pathway. In this review we will focus on these pathways, which are critical for proper protein production, and summarize recent advances in understanding the cotranslational functions and mechanisms of NAC in higher eukaryotes.