Orphan quality control shapes network dynamics and gene expression.

All eukaryotes require intricate protein networks to translate developmental signals into accurate cell fate decisions. Mutations that disturb interactions between network components often result in disease, but how the composition and dynamics of complex networks are established remains poorly understood. Here, we identify the E3 ligase UBR5 as a signaling hub that helps degrade unpaired subunits of multiple transcriptional regulators that act within a network centered on the c-Myc oncoprotein. Biochemical and structural analyses show that UBR5 binds motifs that only become available upon complex dissociation. By rapidly turning over unpaired transcription factor subunits, UBR5 establishes dynamic interactions between transcriptional regulators that allow cells to effectively execute gene expression while remaining receptive to environmental signals. We conclude that orphan quality control plays an essential role in establishing dynamic protein networks, which may explain the conserved need for protein degradation during transcription and offers opportunities to modulate gene expression in disease.

Discovery of Human Signaling Systems: Pairing Peptides to G Protein-Coupled Receptors.

The peptidergic system is the most abundant network of ligand-receptor-mediated signaling in humans. However, the physiological roles remain elusive for numerous peptides and more than 100 G protein-coupled receptors (GPCRs). Here we report the pairing of cognate peptides and receptors. Integrating comparative genomics across 313 species and bioinformatics on all protein sequences and structures of human class A GPCRs, we identify universal characteristics that uncover additional potential peptidergic signaling systems. Using three orthogonal biochemical assays, we pair 17 proposed endogenous ligands with five orphan GPCRs that are associated with diseases, including genetic, neoplastic, nervous and reproductive system disorders. We also identify additional peptides for nine receptors with recognized ligands and pathophysiological roles. This integrated computational and multifaceted experimental approach expands the peptide-GPCR network and opens the way for studies to elucidate the roles of these signaling systems in human physiology and disease. VIDEO ABSTRACT.

GPR146 Deficiency Protects against Hypercholesterolemia and Atherosclerosis.

Although human genetic studies have implicated many susceptible genes associated with plasma lipid levels, their physiological and molecular functions are not fully characterized. Here we demonstrate that orphan G protein-coupled receptor 146 (GPR146) promotes activity of hepatic sterol regulatory element binding protein 2 (SREBP2) through activation of the extracellular signal-regulated kinase (ERK) signaling pathway, thereby regulating hepatic very low-density lipoprotein (VLDL) secretion, and subsequently circulating low-density lipoprotein cholesterol (LDL-C) and triglycerides (TG) levels. Remarkably, GPR146 deficiency reduces plasma cholesterol levels substantially in both wild-type and LDL receptor (LDLR)-deficient mice. Finally, aortic atherosclerotic lesions are reduced by 90% and 70%, respectively, in male and female LDLR-deficient mice upon GPR146 depletion. Taken together, these findings outline a regulatory role for the GPR146/ERK axis in systemic cholesterol metabolism and suggest that GPR146 inhibition could be an effective strategy to reduce plasma cholesterol levels and atherosclerosis.

A hierarchical assembly pathway directs the unique subunit arrangement of TRiC/CCT.

How the essential eukaryotic chaperonin TRiC/CCT assembles from eight distinct subunits into a unique double-ring architecture remains undefined. We show TRiC assembly involves a hierarchical pathway that segregates subunits with distinct functional properties until holocomplex (HC) completion. A stable, likely early intermediate arises from small oligomers containing CCT2, CCT4, CCT5, and CCT7, contiguous subunits that constitute the negatively charged hemisphere of the TRiC chamber, which has weak affinity for unfolded actin. The remaining subunits CCT8, CCT1, CCT3, and CCT6, which comprise the positively charged chamber hemisphere that binds unfolded actin more strongly, join the ring individually. Unincorporated late-assembling subunits are highly labile in cells, which prevents their accumulation and premature substrate binding. Recapitulation of assembly in a recombinant system demonstrates that the subunits in each hemisphere readily form stable, noncanonical TRiC-like HCs with aberrant functional properties. Thus, regulation of TRiC assembly along a biochemical axis disfavors the formation of stable alternative chaperonin complexes.

Quality control of protein complex composition.

Eukaryotic cells possess hundreds of protein complexes that contain multiple subunits and must be formed at the correct time and place during development. Despite specific assembly pathways, cells frequently encounter complexes with missing or aberrant subunits that can disrupt important signaling events. Cells, therefore, employ several ubiquitin-dependent quality control pathways that can prevent, correct, or degrade flawed complexes. In this review, we will discuss our emerging understanding of such quality control of protein complex composition.

NR4A1 regulates expression of immediate early genes, suppressing replication stress in cancer.

Deregulation of oncogenic signals in cancer triggers replication stress. Immediate early genes (IEGs) are rapidly and transiently expressed following stressful signals, contributing to an integrated response. Here, we find that the orphan nuclear receptor NR4A1 localizes across the gene body and 3' UTR of IEGs, where it inhibits transcriptional elongation by RNA Pol II, generating R-loops and accessible chromatin domains. Acute replication stress causes immediate dissociation of NR4A1 and a burst of transcriptionally poised IEG expression. Ectopic expression of NR4A1 enhances tumorigenesis by breast cancer cells, while its deletion leads to massive chromosomal instability and proliferative failure, driven by deregulated expression of its IEG target, FOS. Approximately half of breast and other primary cancers exhibit accessible chromatin domains at IEG gene bodies, consistent with this stress-regulatory pathway. Cancers that have retained this mechanism in adapting to oncogenic replication stress may be dependent on NR4A1 for their proliferation.

Gene therapy for adenosine deaminase severe combined immune deficiency-An unexpected journey of four decades.

Severe combined immune deficiency due to adenosine deaminase deficiency (ADA SCID) is an inborn error of immunity with pan-lymphopenia, due to accumulated cytotoxic adenine metabolites. ADA SCID has been treated using gene therapy with a normal human ADA gene added to autologous hematopoietic stem cells (HSC) for over 30 years. Iterative improvements in vector design, HSC processing methods, and clinical HSC transplant procedures have led nearly all ADA SCID gene therapy patients to achieve consistently beneficial immune restoration with stable engraftment of ADA gene-corrected HSC over the duration of observation (as long as 20 years). One gene therapy for ADA SCID is approved by the European Medicines Agency (EMA) in the European Union (EU) and another is being advanced to licensure in the U.S. and U.K. Despite the clear-cut benefits and safety of this curative gene and cell therapy, it remains challenging to achieve sustained availability and access, especially for rare disorders like ADA SCID.

The role of omics in improving the orphan crop tef.

Tef or teff [Eragrostis tef (Zucc.) Trotter] is a cereal crop indigenous to the Horn of Africa, where it is a staple food for a large population. The popularity of tef arises from its resilience to environmental stresses and its nutritional value. For many years, tef has been considered an orphan crop, but recent research initiatives from across the globe are helping to unravel its undisclosed potential. Advanced omics tools and techniques have been directed toward the exploration of tef's diversity with the aim of increasing its productivity. In this review, we report on the most recent advances in tef omics that brought the crop into the spotlight of international research.

oskar acts with the transcription factor Creb to regulate long-term memory in crickets.

Novel genes have the potential to drive the evolution of new biological mechanisms, or to integrate into preexisting regulatory circuits and contribute to the regulation of older, conserved biological functions. One such gene, the novel insect-specific gene oskar, was first identified based on its role in establishing the Drosophila melanogaster germ line. We previously showed that this gene likely arose through an unusual domain transfer event involving bacterial endosymbionts and played a somatic role before evolving its well-known germ line function. Here, we provide empirical support for this hypothesis in the form of evidence for a neural role for oskar. We show that oskar is expressed in the adult neural stem cells of a hemimetabolous insect, the cricket Gryllus bimaculatus. In these stem cells, called neuroblasts, oskar is required together with the ancient animal transcription factor Creb to regulate long-term (but not short-term) olfactory memory. We provide evidence that oskar positively regulates Creb, which plays a conserved role in long-term memory across animals, and that oskar in turn may be a direct target of Creb. Together with previous reports of a role for oskar in nervous system development and function in crickets and flies, our results are consistent with the hypothesis that oskar's original somatic role may have been in the insect nervous system. Moreover, its colocalization and functional cooperation with the conserved pluripotency gene piwi in the nervous system may have facilitated oskar's later co-option to the germ line in holometabolous insects.

Steroidogenic factor 1 (SF-1; Nr5a1) regulates the formation of the ovarian reserve.

The ovarian follicle reserve, formed pre- or perinatally, comprises all oocytes for lifetime reproduction. Depletion of this reserve results in infertility. Steroidogenic factor 1 (SF-1; Nr5a1) and liver receptor homolog 1 (LRH-1; Nr5a2) are two orphan nuclear receptors that regulate adult endocrine function, but their role in follicle formation is unknown. We developed models of conditional depletion of SF-1 or LRH-1 from prenatal ovaries. Depletion of SF-1, but not LRH-1, resulted in dramatically smaller ovaries and fewer primordial follicles. This was mediated by increased oocyte death, resulting from increased ovarian inflammation and increased Notch signaling. Major dysregulated genes were Iroquois homeobox 3 and 5 and their downstream targets involved in the establishment of the ovarian laminin matrix and oocyte-granulosa cell gap junctions. Disruptions of these pathways resulted in follicles with impaired basement membrane formation and compromised oocyte-granulosa communication networks, believed to render them more prone to atresia. This study identifies SF-1 as a key regulator of the formation of the ovarian reserve.

A distinct human cell type expressing MHCII and RORγt with dual characteristics of dendritic cells and type 3 innate lymphoid cells.

Recent studies have characterized various mouse antigen-presenting cells (APCs) expressing the lymphoid-lineage transcription factor RORγt (Retinoid-related orphan receptor gamma t), which exhibit distinct phenotypic features and are implicated in the induction of peripheral regulatory T cells (Tregs) and immune tolerance to microbiota and self-antigens. These APCs encompass Janus cells and Thetis cell subsets, some of which express the AutoImmune REgulator (AIRE). RORγt+ MHCII+ type 3 innate lymphoid cells (ILC3) have also been implicated in the instruction of microbiota-specific Tregs. While RORγt+ APCs have been actively investigated in mice, the identity and function of these cell subsets in humans remain elusive. Herein, we identify a rare subset of RORγt+ cells with dendritic cell (DC) features through integrated single-cell RNA sequencing and single-cell ATAC sequencing. These cells, which we term RORγt+ DC-like cells (R-DC-like), exhibit DC morphology, express the MHC class II machinery, and are distinct from all previously reported DC and ILC3 subsets, but share transcriptional and epigenetic similarities with DC2 and ILC3. We have developed procedures to isolate and expand them in vitro, enabling their functional characterization. R-DC-like cells proliferate in vitro, continue to express RORγt, and differentiate into CD1c+ DC2-like cells. They stimulate the proliferation of allogeneic T cells. The identification of human R-DC-like cells with proliferative potential and plasticity toward CD1c+ DC2-like cells will prompt further investigation into their impact on immune homeostasis, inflammation, and autoimmunity.

An orphan gene enhances male reproductive success in Plutella xylostella.

Plutella xylostella exhibits exceptional reproduction ability, yet the genetic basis underlying the high reproductive capacity remains unknown. Here, we demonstrate that an orphan gene, lushu, which encodes a sperm protein, plays a crucial role in male reproductive success. Lushu is located on the Z chromosome and is prevalent across different P. xylostella populations worldwide. We subsequently generated lushu mutants using transgenic CRISPR/Cas9 system. Knockout of Lushu results in reduced male mating efficiency and accelerated death in adult males. Furthermore, our findings highlight that the deficiency of lushu reduced the transfer of sperms from males to females, potentially resulting in hindered sperm competition. Additionally, the knockout of Lushu results in disrupted gene expression in energy-related pathways and elevated insulin levels in adult males. Our findings reveal that male reproductive performance has evolved through the birth of a newly evolved, lineage-specific gene with enormous potentiality in fecundity success. These insights hold valuable implications for identifying the target for genetic control, particularly in relation to species-specific traits that are pivotal in determining high levels of fecundity.

Emergence of an Orphan Nitrogenase Protein Following Atmospheric Oxygenation.

Molecular innovations within key metabolisms can have profound impacts on element cycling and ecological distribution. Yet, much of the molecular foundations of early evolved enzymes and metabolisms are unknown. Here, we bring one such mystery to relief by probing the birth and evolution of the G-subunit protein, an integral component of certain members of the nitrogenase family, the only enzymes capable of biological nitrogen fixation. The G-subunit is a Paleoproterozoic-age orphan protein that appears more than 1 billion years after the origin of nitrogenases. We show that the G-subunit arose with novel nitrogenase metal dependence and the ecological expansion of nitrogen-fixing microbes following the transition in environmental metal availabilities and atmospheric oxygenation that began ∼2.5 billion years ago. We identify molecular features that suggest early G-subunit proteins mediated cofactor or protein interactions required for novel metal dependency, priming ancient nitrogenases and their hosts to exploit these newly diversified geochemical environments. We further examined the degree of functional specialization in G-subunit evolution with extant and ancestral homologs using laboratory reconstruction experiments. Our results indicate that permanent recruitment of the orphan protein depended on the prior establishment of conserved molecular features and showcase how contingent evolutionary novelties might shape ecologically important microbial innovations.

A genome sequencing system for universal newborn screening, diagnosis, and precision medicine for severe genetic diseases.

Newborn screening (NBS) dramatically improves outcomes in severe childhood disorders by treatment before symptom onset. In many genetic diseases, however, outcomes remain poor because NBS has lagged behind drug development. Rapid whole-genome sequencing (rWGS) is attractive for comprehensive NBS because it concomitantly examines almost all genetic diseases and is gaining acceptance for genetic disease diagnosis in ill newborns. We describe prototypic methods for scalable, parentally consented, feedback-informed NBS and diagnosis of genetic diseases by rWGS and virtual, acute management guidance (NBS-rWGS). Using established criteria and the Delphi method, we reviewed 457 genetic diseases for NBS-rWGS, retaining 388 (85%) with effective treatments. Simulated NBS-rWGS in 454,707 UK Biobank subjects with 29,865 pathogenic or likely pathogenic variants associated with 388 disorders had a true negative rate (specificity) of 99.7% following root cause analysis. In 2,208 critically ill children with suspected genetic disorders and 2,168 of their parents, simulated NBS-rWGS for 388 disorders identified 104 (87%) of 119 diagnoses previously made by rWGS and 15 findings not previously reported (NBS-rWGS negative predictive value 99.6%, true positive rate [sensitivity] 88.8%). Retrospective NBS-rWGS diagnosed 15 children with disorders that had been undetected by conventional NBS. In 43 of the 104 children, had NBS-rWGS-based interventions been started on day of life 5, the Delphi consensus was that symptoms could have been avoided completely in seven critically ill children, mostly in 21, and partially in 13. We invite groups worldwide to refine these NBS-rWGS conditions and join us to prospectively examine clinical utility and cost effectiveness.

Identification of a novel neurovirulence factor encoded by the cryptic orphan gene UL31.6 of herpes simplex virus 1.

Although the herpes simplex virus type 1 (HSV-1) genome was thought to contain approximately 80 different protein coding sequences (CDSs), recent multi-omics analyses reported HSV-1 encodes more than 200 potential CDSs. However, few of the newly identified CDSs were confirmed to be expressed at the peptide or protein level in HSV-1-infected cells. Furthermore, the impact of the proteins they encode on HSV-1 infection is largely unknown. This study focused on a newly identified CDS, UL31.6. Re-analyzation of our previous chemical proteomics data verified that UL31.6 was expressed at the peptide level in HSV-1-infected cells. Antisera raised against a viral protein encoded by UL31.6 (pUL31.6) reacted with a protein with an approximate molecular mass of 37 kDa in lysates of Vero cells infected with each of three HSV-1 strains. pUL31.6 was efficiently dissociated from virions in high-salt solution. A UL31.6-null mutation had a minimal effect on HSV-1 gene expression, replication, cell-to-cell spread, and morphogenesis in Vero cells; in contrast, it significantly reduced HSV-1 cell-to-cell spread in three neural cells but not in four non-neural cells including Vero cells. The UL31.6-null mutation also significantly reduced the mortality and viral replication in the brains of mice after intracranial infection, but had minimal effects on pathogenic manifestations in and around the eyes, and viral replication detected in the tear films of mice after ocular infection. These results indicated that pUL31.6 was a tegument protein and specifically acted as a neurovirulence factor by potentially promoting viral transmission between neuronal cells in the central nervous system.IMPORTANCERecent multi-omics analyses reported the herpes simplex virus type 1 (HSV-1) genome encodes an additional number of potential coding sequences (CDSs). However, the expressions of these CDSs at the peptide or protein levels and the biological effects of these CDSs on HSV-1 infection remain largely unknown. This study annotated a cryptic orphan CDS, termed UL31.6, an HSV-1 gene that encodes a tegument protein with an approximate molecular mass of 37 kDa, which specifically acts as a neurovirulence factor. Our study indicates that HSV-1 proteins important for viral pathogenesis remain to be identified and a comprehensive understanding of the pathogenesis of HSV-1 will require not only the identification of cryptic orphan CDSs using emerging technologies but also step-by-step and in-depth analyses of each of the cryptic orphan CDSs.

Improved structure-related prediction for insufficient homologous proteins using MSA enhancement and pre-trained language model.

In recent years, protein structure problems have become a hotspot for understanding protein folding and function mechanisms. It has been observed that most of the protein structure works rely on and benefit from co-evolutionary information obtained by multiple sequence alignment (MSA). As an example, AlphaFold2 (AF2) is a typical MSA-based protein structure tool which is famous for its high accuracy. As a consequence, these MSA-based methods are limited by the quality of the MSAs. Especially for orphan proteins that have no homologous sequence, AlphaFold2 performs unsatisfactorily as MSA depth decreases, which may pose a barrier to its widespread application in protein mutation and design problems in which there are no rich homologous sequences and rapid prediction is needed. In this paper, we constructed two standard datasets for orphan and de novo proteins which have insufficient/none homology information, called Orphan62 and Design204, respectively, to fairly evaluate the performance of the various methods in this case. Then, depending on whether or not utilizing scarce MSA information, we summarized two approaches, MSA-enhanced and MSA-free methods, to effectively solve the issue without sufficient MSAs. MSA-enhanced model aims to improve poor MSA quality from the data source by knowledge distillation and generation models. MSA-free model directly learns the relationship between residues on enormous protein sequences from pre-trained models, bypassing the step of extracting the residue pair representation from MSA. Next, we evaluated the performance of four MSA-free methods (trRosettaX-Single, TRFold, ESMFold and ProtT5) and MSA-enhanced (Bagging MSA) method compared with a traditional MSA-based method AlphaFold2, in two protein structure-related prediction tasks, respectively. Comparison analyses show that trRosettaX-Single and ESMFold which belong to MSA-free method can achieve fast prediction ($\sim\! 40$s) and comparable performance compared with AF2 in tertiary structure prediction, especially for short peptides, $\alpha $-helical segments and targets with few homologous sequences. Bagging MSA utilizing MSA enhancement improves the accuracy of our trained base model which is an MSA-based method when poor homology information exists in secondary structure prediction. Our study provides biologists an insight of how to select rapid and appropriate prediction tools for enzyme engineering and peptide drug development. CONTACT: guofei@csu.edu.cn, jj.tang@siat.ac.cn.

Metabolism of Free Guanidine in Bacteria Is Regulated by a Widespread Riboswitch Class.

The guanidyl moiety is a component of fundamental metabolites, including the amino acid arginine, the energy carrier creatine, and the nucleobase guanine. Curiously, reports regarding the importance of free guanidine in biology are sparse, and no biological receptors that specifically recognize this compound have been previously identified. We report that many members of the ykkC motif RNA, the longest unresolved riboswitch candidate, naturally sense and respond to guanidine. This RNA is found throughout much of the bacterial domain of life, where it commonly controls the expression of proteins annotated as urea carboxylases and multidrug efflux pumps. Our analyses reveal that these proteins likely function as guanidine carboxylases and guanidine transporters, respectively. Furthermore, we demonstrate that bacteria are capable of endogenously producing guanidine. These and related findings demonstrate that free guanidine is a biologically relevant compound, and several gene families that can alleviate guanidine toxicity exist.

The combined action of Esrrb and Nr5a2 is essential for murine naïve pluripotency.

The maintenance of pluripotency in mouse embryonic stem cells (ESCs) is governed by the action of an interconnected network of transcription factors. Among them, only Oct4 and Sox2 have been shown to be strictly required for the self-renewal of ESCs and pluripotency, particularly in culture conditions in which differentiation cues are chemically inhibited. Here, we report that the conjunct activity of two orphan nuclear receptors, Esrrb and Nr5a2, parallels the importance of that of Oct4 and Sox2 in naïve mouse ESCs. By occupying a large common set of regulatory elements, these two factors control the binding of Oct4, Sox2 and Nanog to DNA. Consequently, in their absence the pluripotency network collapses and the transcriptome is substantially deregulated, leading to the differentiation of ESCs. Altogether, this work identifies orphan nuclear receptors, previously thought to be performing supportive functions, as a set of core regulators of naïve pluripotency.

Oxamic transcarbamylase of Escherichia coli is encoded by the three genes allFGH (formerly fdrA, ylbE, and ylbF).

Escherichia coli uses allantoin as the sole nitrogen source during anaerobic growth. In the final step of allantoin degradation, oxamic transcarbamylase (OXTCase) converts oxalurate to carbamoyl phosphate (CP) and oxamate. The activity of this enzyme was first measured in Streptococcus allantoicus in the 1960s, but no OXTCase enzyme or the encoding gene(s) have been found in any strain. This study discovered that allFGH (fdrA, ylbE, and ylbF) are the genes that encode the global orphan enzyme OXTCase. The three genes form an operon together with allK (ybcF), encoding catabolic carbamate kinase. The allFGHK operon is located directly downstream of the allECD operon that encodes enzymes for the preceding steps of OXTCase. The OXTCase kinetic parameters were analyzed using the purified protein composed of AllF-AllG-AllH (FdrA-YlbE-YlbF); for the substrate CP, KM and Vmax were 1.3 mM and 15.4 U/mg OXTCase, respectively, and for the substrate oxamate, they were 36.9 mM and 27.0 U/mg OXTCase. In addition, the OXTCase encoded by the three genes is a novel transcarbamylase that shows no similarity with known enzymes of the transcarbamylase family such as aspartate transcarbamylase, ornithine transcarbamylase, and YgeW transcarbamylase. The present study elucidated the anaerobic allantoin degradation pathway of E. coli. Therefore, we suggest that the genes fdrA, ylbE, and ylbF are renamed allF, allG, and allH, respectively.IMPORTANCEThe anaerobic allantoin degradation pathway of Escherichia coli includes a global orphan enzyme, oxamic transcarbamylase (OXTCase), which converts oxalurate to carbamoyl phosphate and oxamate. This study found that the allFGH (fdrA, ylbE, and ylbF) genes encode OXTCase. The OXTCase activity and kinetics were successfully determined with purified recombinant AllF-AllG-AllH (FdrA-YlbE-YlbF). This OXTCase is a novel transcarbamylase that shows no similarity with known enzymes of the transcarbamylase family such as aspartate transcarbamylase (ATCase), ornithine transcarbamylase (OTCase), and YgeW transcarbamylase (YTCase). In addition, OXTCase activity requires three genes, whereas ATCase is encoded by two genes, and OTCase and YTCase are encoded by a single gene. The current study discovered OXTCase, the last unknown step in allantoin degradation, and this enzyme is a new member of the transcarbamylase group that was previously unknown.

The Marssonina rosae effector MrSEP43 suppresses rose immunity by targeting the orphan protein RcBROG.

Rose black spot disease, caused by Marssonina rosae (syn. Diplocarpon rosae), is one of the most widespread diseases of field-grown roses worldwide. Pathogens have been found to interfere with or stimulate plant immune response through the secreted effectors. However, the molecular mechanism involved in inhibition of rose immune response by M. rosae effectors remains poorly understood. In this study, we identified the effector MrSEP43, which played a pivotal role in promoting the virulence of M. rosae and enhancing rose susceptibility by reducing callose deposition, H2O2 accumulation, and the expression of defense genes in jasmonic acid signaling pathway. Through Y2H, BiFC, and LUC assays, MrSEP43 was proved to interact with the rose orphan protein RcBROG. RcBROG, which was a positive regulator of defense against M. rosae, enhanced rose resistance by increasing callose deposition, H2O2 accumulation, and expression of RcERF1 in the ethylene signaling pathway. Overall, our findings suggested that the virulence effector MrSEP43 from M. rosae specifically targeted the orphan protein RcBROG to suppress rose immune response to M. rosae. These results provided new insight into how M. rosae manipulated and successfully colonized rose leaves, and were essential for preventing the breakdown of resistance to rose black spot disease.