Heat shock protein 90 (Hsp90) is an ATP-dependent molecular chaperone which is essential in eukaryotes. It is required for the activation and stabilization of a wide variety of client proteins and ...many of them are involved in important cellular pathways. Since Hsp90 affects numerous physiological processes such as signal transduction, intracellular transport, and protein degradation, it became an interesting target for cancer therapy. Structurally, Hsp90 is a flexible dimeric protein composed of three different domains which adopt structurally distinct conformations. ATP binding triggers directionality in these conformational changes and leads to a more compact state. To achieve its function, Hsp90 works together with a large group of cofactors, termed co-chaperones. Co-chaperones form defined binary or ternary complexes with Hsp90, which facilitate the maturation of client proteins. In addition, posttranslational modifications of Hsp90, such as phosphorylation and acetylation, provide another level of regulation. They influence the conformational cycle, co-chaperone interaction, and inter-domain communications. In this review, we discuss the recent progress made in understanding the Hsp90 machinery.
Runt-related transcription factor 2 (Runx2) transactivates many genes required for osteoblast differentiation. The role of N-α-acetyltransferase 10 (NAA10, arrest-defective-1), originally identified ...in yeast, remains poorly understood in mammals. Here we report a new NAA10 function in Runx2-mediated osteogenesis. Runx2 stabilizes NAA10 in osteoblasts during BMP-2-induced differentiation, and NAA10 in turn controls this differentiation by inhibiting Runx2. NAA10 delays bone healing in a rat calvarial defect model and bone development in neonatal mice. Mechanistically, NAA10 acetylates Runx2 at Lys225, and this acetylation inhibits Runx2-driven transcription by interfering with CBFβ binding to Runx2. Our study suggests that NAA10 acts as a guard ensuring balanced osteogenesis by fine-tuning Runx2 signalling in a feedback manner. NAA10 inhibition could be considered a potential strategy for facilitating bone formation.
N-terminal acetylation is a conserved protein modification among eukaryotes. The yeast Saccharomyces cerevisiae is a valuable model system for studying this modification. The bulk of protein ...N-terminal acetylation in S. cerevisiae is catalyzed by the N-terminal acetyltransferases NatA, NatB, and NatC. Thus far, proteome-wide identification of the in vivo protein substrates of yeast NatA and NatB has been performed by N-terminomics. Here, we used S. cerevisiae deleted for the NatC catalytic subunit Naa30 and identified 57 yeast NatC substrates by N-terminal combined fractional diagonal chromatography analysis. Interestingly, in addition to the canonical N-termini starting with ML, MI, MF, and MW, yeast NatC substrates also included MY, MK, MM, MA, MV, and MS. However, for some of these substrate types, such as MY, MK, MV, and MS, we also uncovered (residual) non-NatC NAT activity, most likely due to the previously established redundancy between yeast NatC and NatE/Naa50. Thus, we have revealed a complex interplay between different NATs in targeting methionine-starting N-termini in yeast. Furthermore, our results showed that ectopic expression of human NAA30 rescued known NatC phenotypes in naa30Δ yeast, as well as partially restored the yeast NatC Nt-acetylome. Thus, we demonstrate an evolutionary conservation of NatC from yeast to human thereby underpinning future disease models to study pathogenic NAA30 variants. Overall, this work offers increased biochemical and functional insights into NatC-mediated N-terminal acetylation and provides a basis for future work to pinpoint the specific molecular mechanisms that link the lack of NatC-mediated N-terminal acetylation to phenotypes of NatC deletion yeast.
ABSTRACT
N‐terminal acetylation is a common protein modification in eukaryotes associated with numerous cellular processes. Inherited mutations in NAA10, encoding the catalytic subunit of the major ...N‐terminal acetylation complex NatA have been associated with diverse, syndromic X‐linked recessive disorders, whereas de novo missense mutations have been reported in one male and one female individual with severe intellectual disability but otherwise unspecific phenotypes. Thus, the full genetic and clinical spectrum of NAA10 deficiency is yet to be delineated. We identified three different novel and one known missense mutation in NAA10, de novo in 11 females, and due to maternal germ line mosaicism in another girl and her more severely affected and deceased brother. In vitro enzymatic assays for the novel, recurrent mutations p.(Arg83Cys) and p.(Phe128Leu) revealed reduced catalytic activity. X‐inactivation was random in five females. The core phenotype of X‐linked NAA10‐related N‐terminal‐acetyltransferase deficiency in both males and females includes developmental delay, severe intellectual disability, postnatal growth failure with severe microcephaly, and skeletal or cardiac anomalies. Genotype–phenotype correlations within and between both genders are complex and may include various factors such as location and nature of mutations, enzymatic stability and activity, and X‐inactivation in females.
We identified de novo mutations in the NAA10 gene located on the X‐chromosome in 12 girls with severe intellectual disability (ID), microcephaly, growth retardation and further anomalies. The NAA10 enzyme is involved in N‐terminal acetylation of a large number of proteins. Previously, mutations in NAA10 had been mainly known to cause X‐linked recessive syndromic ID disorders in males. Our study redefines the clinical spectrum of NAA10 related N‐terminal‐acetyltransferase deficiency, a relatively frequent cause of ID in girls.
The human N-terminal acetyltransferase E (NatE) contains NAA10 and NAA50 catalytic, and NAA15 auxiliary subunits and associates with HYPK, a protein with intrinsic NAA10 inhibitory activity. NatE ...co-translationally acetylates the N-terminus of half the proteome to mediate diverse biological processes, including protein half-life, localization, and interaction. The molecular basis for how NatE and HYPK cooperate is unknown. Here, we report the cryo-EM structures of human NatE and NatE/HYPK complexes and associated biochemistry. We reveal that NAA50 and HYPK exhibit negative cooperative binding to NAA15 in vitro and in human cells by inducing NAA15 shifts in opposing directions. NAA50 and HYPK each contribute to NAA10 activity inhibition through structural alteration of the NAA10 substrate-binding site. NAA50 activity is increased through NAA15 tethering, but is inhibited by HYPK through structural alteration of the NatE substrate-binding site. These studies reveal the molecular basis for coordinated N-terminal acetylation by NatE and HYPK.
Diet-induced obesity can be caused by impaired thermogenesis of beige adipocytes, the brown-like adipocytes in white adipose tissue (WAT). Promoting brown-like features in WAT has been an attractive ...therapeutic approach for obesity. However, the mechanism underlying beige adipocyte formation is largely unknown. N-α-acetyltransferase 10 protein (Naa10p) catalyzes N-α-acetylation of nascent proteins, and overexpression of human Naa10p is linked to cancer development. Here, we report that both conventional and adipose-specific Naa10p deletions in mice result in increased energy expenditure, thermogenesis, and beige adipocyte differentiation. Mechanistically, Naa10p acetylates the N terminus of Pgc1α, which prevents Pgc1α from interacting with Pparγ to activate key genes, such as Ucp1, involved in beige adipocyte function. Consistently, fat tissues of obese human individuals show higher NAA10 expression. Thus, Naa10p-mediated N-terminal acetylation of Pgc1α downregulates thermogenic gene expression, making inhibition of Naa10p enzymatic activity a potential strategy for treating obesity.
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•Adipose-specific Naa10p depletion prevents diet-induced obesity•Naa10p depletion increases Ucp1 expression and thermogenesis in beige adipocytes•N-terminal acetylation of Pgc1α by Naa10p suppresses thermogenic gene expression•Higher NAA10 expression correlates with human obesity
Lee et al. reveal that Naa10p-mediated N-terminal acetylation of Pgc1α inhibits beige thermogenesis and promotes diet-induced obesity (DIO) in mice. Together with the fact that NAA10 expression positively correlates with human obesity, their results suggest that inhibiting the enzymatic activity of Naa10p in adipose tissues may suppress DIO.
NatA co-translationally acetylates the N termini of over 40% of eukaryotic proteins and can associate with another catalytic subunit, Naa50, to form a ternary NatA/Naa50 dual enzyme complex (also ...called NatE). The molecular basis of association between Naa50 and NatA and the mechanism for how their association affects their catalytic activities in yeast and human are poorly understood. Here, we determined the X-ray crystal structure of yeast NatA/Naa50 as a scaffold to understand coregulation of NatA/Naa50 activity in both yeast and human. We find that Naa50 makes evolutionarily conserved contacts to both the Naa10 and Naa15 subunits of NatA. These interactions promote catalytic crosstalk within the human complex, but do so to a lesser extent in the yeast complex, where Naa50 activity is compromised. These studies have implications for understanding the role of the NatA/Naa50 complex in modulating the majority of the N-terminal acetylome in diverse species.
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•NatA/Naa50 forms a stable complex through evolutionarily conserved interactions•NatA-Naa50 interactions promote catalytic crosstalk between Naa10 and Naa50•Yeast Naa50 is defective in activity due to compromised substrate binding•Evolutionarily conserved Naa15 TY mutants can disrupt NatA-Naa50 association
The NatA/Naa50 complex contains two catalytic subunits and one auxiliary subunit for co-translational N-terminal acetylation. Deng et al. describe the X-ray crystal structure of yeast NatA/Naa50 and use it as a scaffold to uncover evolutionarily conserved catalytic crosstalk within the orthologous complexes in yeast and human.
N-alpha-acetylation is a common co-translational protein modification that is essential for normal cell function in humans. We previously identified the genetic basis of an X-linked infantile lethal ...Mendelian disorder involving a c.109T>C (p.Ser37Pro) missense variant in NAA10, which encodes the catalytic subunit of the N-terminal acetyltransferase A (NatA) complex. The auxiliary subunit of the NatA complex, NAA15, is the dimeric binding partner for NAA10. Through a genotype-first approach with whole-exome or genome sequencing (WES/WGS) and targeted sequencing analysis, we identified and phenotypically characterized 38 individuals from 33 unrelated families with 25 different de novo or inherited, dominantly acting likely gene disrupting (LGD) variants in NAA15. Clinical features of affected individuals with LGD variants in NAA15 include variable levels of intellectual disability, delayed speech and motor milestones, and autism spectrum disorder. Additionally, mild craniofacial dysmorphology, congenital cardiac anomalies, and seizures are present in some subjects. RNA analysis in cell lines from two individuals showed degradation of the transcripts with LGD variants, probably as a result of nonsense-mediated decay. Functional assays in yeast confirmed a deleterious effect for two of the LGD variants in NAA15. Further supporting a mechanism of haploinsufficiency, individuals with copy-number variant (CNV) deletions involving NAA15 and surrounding genes can present with mild intellectual disability, mild dysmorphic features, motor delays, and decreased growth. We propose that defects in NatA-mediated N-terminal acetylation (NTA) lead to variable levels of neurodevelopmental disorders in humans, supporting the importance of the NatA complex in normal human development.
Cotranslational N‐terminal (Nt‐) acetylation of nascent polypeptides is mediated by N‐terminal acetyltransferases (NATs). The very N‐terminal amino acid sequence largely determines whether or not a ...given protein is Nt‐acetylated. Currently, there are six distinct NATs characterized, NatA‐NatF, in humans of which the in vivo substrate specificity of Naa50 (Nat5)/NatE, an alternative catalytic subunit of the human NatA, so far remained elusive. In this study, we quantitatively compared the Nt‐acetylomes of wild‐type yeast S. cerevisiae expressing the endogenous yeast Naa50 (yNaa50), the congenic strain lacking yNaa50, and an otherwise identical strain expressing human Naa50 (hNaa50). Six canonical yeast NatA substrates were Nt‐acetylated less in yeast lacking yNaa50 than in wild‐type yeast. In contrast, the ectopically expressed hNaa50 resulted, predominantly, in the Nt‐acetylation of N‐terminal Met (iMet) starting N‐termini, including iMet‐Lys, iMet‐Val, iMet‐Ala, iMet‐Tyr, iMet‐Phe, iMet‐Leu, iMet‐Ser, and iMet‐Thr N‐termini. This identified hNaa50 as being similar, in its substrate specificity, to the previously characterized hNaa60/NatF. In addition, the identification, in yNaa50‐lacking yeast expressing hNaa50, of Nt‐acetylated iMet followed by a small residue such as Ser, Thr, Ala, or Val, revealed a kinetic competition between Naa50 and Met‐aminopeptidases (MetAPs), and implied that Nt‐acetylated iMet followed by a small residue cannot be removed by MetAPs, a deduction supported by our in vitro data. As such, Naa50‐mediated Nt‐acetylation may act to retain the iMet of proteins of otherwise MetAP susceptible N‐termini and the fraction of retained and Nt‐acetylated iMet (followed by a small residue) in such a setting would be expected to depend on the relative levels of ribosome‐associated Naa50/NatA and MetAPs.
Amino-terminal acetylation is a ubiquitous modification in eukaryotes that is involved in a growing number of biological processes.There are six known eukaryotic amino-terminal acetyltransferases ...(NATs), which are differentiated from one another on the basis of substrate specificity. To date, two eukaryotic NATs, NatA and NatE, have been structurally characterized, of which NatA will acetylate the α-amino group of a number of nonmethionine amino-terminal residue substrates such as serine; NatE requires a substrate amino-terminal methionine residue for activity. Interestingly, these two NATs use different catalytic strategies to accomplish substrate-specific acetylation. In archaea, where this modification is less prevalent, only one NAT enzyme has been identified. Surprisingly, this enzyme is able to acetylate NatA and NatE substrates and is believed to represent an ancestral NAT variant from which the eukaryotic NAT machinery evolved. To gain insight into the evolution of NAT enzymes, we determined the X-ray crystal structure of an archaeal NAT from Sulfolobus solfataricus (ssNAT). Through the use of mutagenesis and kinetic analysis, we show that the active site of ssNAT represents a hybrid of the NatA and NatE active sites, and we highlight features of this protein that allow it to facilitate catalysis of distinct substrates through different catalytic strategies, which is a unique characteristic of this enzyme. Taken together, the structural and biochemical data presented here have implications for the evolution of eukaryotic NAT enzymes and the substrate specificities therein.
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