skip to main content

Title: Comparative Analysis and Ancestral Sequence Reconstruction of Bacterial Sortase Family Proteins Generates Functional Ancestral Mutants with Different Sequence Specificities
Gram-positive bacteria are some of the earliest known life forms, diverging from gram-negative bacteria 2 billion years ago. These organisms utilize sortase enzymes to attach proteins to their peptidoglycan cell wall, a structural feature that distinguishes the two types of bacteria. The transpeptidase activity of sortases make them an important tool in protein engineering applications, e.g., in sortase-mediated ligations or sortagging. However, due to relatively low catalytic efficiency, there are ongoing efforts to create better sortase variants for these uses. Here, we use bioinformatics tools, principal component analysis and ancestral sequence reconstruction, in combination with protein biochemistry, to analyze natural sequence variation in these enzymes. Principal component analysis on the sortase superfamily distinguishes previously described classes and identifies regions of relatively high sequence variation in structurally-conserved loops within each sortase family, including those near the active site. Using ancestral sequence reconstruction, we determined sequences of ancestral Staphylococcus and Streptococcus Class A sortase proteins. Enzyme assays revealed that the ancestral Streptococcus enzyme is relatively active and shares similar sequence variation with other Class A Streptococcus sortases. Taken together, we highlight how natural sequence variation can be utilized to investigate this important protein family, arguing that these and similar techniques may be used to discover or design sortases with increased catalytic efficiency and/or selectivity for sortase-mediated ligation experiments.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Page Range / eLocation ID:
121 to 135
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Summary

    Proper protein anchoring is key to the biogenesis of prokaryotic cell surfaces, dynamic, resilient structures that play crucial roles in various cell processes. A novel surface protein anchoring mechanism inHaloferax volcaniidepends upon the peptidase archaeosortase A (ArtA) processing C‐termini of substrates containing C‐terminal tripartite structures and anchoring mature substrates to the cell membrane via intercalation of lipid‐modified C‐terminal amino acid residues. While this membrane protein lacks clear homology to soluble sortase transpeptidases of Gram‐positive bacteria, which also process C‐termini of substrates whose C‐terminal tripartite structures resemble those of ArtA substrates, archaeosortases do contain conserved cysteine, arginine and arginine/histidine/asparagine residues, reminiscent of His‐Cys‐Arg residues of sortase catalytic sites. The study presented here shows that ArtAWT‐GFP expressedin transcomplements ΔartAgrowth and motility phenotypes, while alanine substitution mutants, Cys173(C173A), Arg214(R214A) or Arg253(R253A), and the serine substitution mutant for Cys173(C173S), fail to complement these phenotypes. Consistent with sortase active site replacement mutants, ArtAC173A‐GFP, ArtAC173S‐GFP and ArtAR214A‐GFP cannot process substrates, while replacement of the third residue, ArtAR253A‐GFP retains some processing activity. These findings support the view that similarities between certain aspects of the structures and functions of the sortases and archaeosortases are the result of convergent evolution.

    more » « less
  2. Billions of years ago, the Earth’s atmosphere had very little oxygen. It was only after some bacteria and early plants evolved to harness energy from sunlight that oxygen began to fill the Earth’s environment. Oxygen is highly reactive and can interfere with enzymes and other molecules that are essential to life. Organisms living at this point in history therefore had to adapt to survive in this new oxygen-rich world. An ancient family of enzymes known as ribonucleotide reductases are used by all free-living organisms and many viruses to repair and replicate their DNA. Because of their essential role in managing DNA, these enzymes have been around on Earth for billions of years. Understanding how they evolved could therefore shed light on how nature adapted to increasing oxygen levels and other environmental changes at the molecular level. One approach to study how proteins evolved is to use computational analysis to construct a phylogenetic tree. This reveals how existing members of a family are related to one another based on the chain of molecules (known as amino acids) that make up each protein. Despite having similar structures and all having the same function, ribonucleotide reductases have remarkably diverse sequences of amino acids. This makes it computationally very demanding to build a phylogenetic tree. To overcome this, Burnim, Spence, Xu et al. created a phylogenetic tree using structural information from a part of the enzyme that is relatively similar in many modern-day ribonucleotide reductases. The final result took seven continuous months on a supercomputer to generate, and includes over 6,000 members of the enzyme family. The phylogenetic tree revealed a new distinct group of ribonucleotide reductases that may explain how one adaptation to increasing levels of oxygen emerged in some family members, while another adaptation emerged in others. The approach used in this work also opens up a new way to study how other highly diverse enzymes and other protein families evolved, potentially revealing new insights about our planet’s past. 
    more » « less
  3. Abstract

    TEM-1 β-lactamase degrades β-lactam antibiotics with a strong preference for penicillins. Sequence reconstruction studies indicate that it evolved from ancestral enzymes that degraded a variety of β-lactam antibiotics with moderate efficiency. This generalist to specialist conversion involved more than 100 mutational changes, but conserved fold and catalytic residues, suggesting a role for dynamics in enzyme evolution. Here, we develop a conformational dynamics computational approach to rationally mold a protein flexibility profile on the basis of a hinge-shift mechanism. By deliberately weighting and altering the conformational dynamics of a putative Precambrian β-lactamase, we engineer enzyme specificity that mimics the modern TEM-1 β-lactamase with only 21 amino acid replacements. Our conformational dynamics design thus re-enacts the evolutionary process and provides a rational allosteric approach for manipulating function while conserving the enzyme active site.

    more » « less
  4. Abstract

    The nitrogenase metalloenzyme family, essential for supplying fixed nitrogen to the biosphere, is one of life's key biogeochemical innovations. The three forms of nitrogenase differ in their metal dependence, each binding either a FeMo‐, FeV‐, or FeFe‐cofactor where the reduction of dinitrogen takes place. The history of nitrogenase metal dependence has been of particular interest due to the possible implication that ancient marine metal availabilities have significantly constrained nitrogenase evolution over geologic time. Here, we reconstructed the evolutionary history of nitrogenases, and combined phylogenetic reconstruction, ancestral sequence inference, and structural homology modeling to evaluate the potential metal dependence of ancient nitrogenases. We find that active‐site sequence features can reliably distinguish extant Mo‐nitrogenases from V‐ and Fe‐nitrogenases and that inferred ancestral sequences at the deepest nodes of the phylogeny suggest these ancient proteins most resemble modern Mo‐nitrogenases. Taxa representing early‐branching nitrogenase lineages lack one or more biosyntheticnifEandnifNgenes that both contribute to the assembly of the FeMo‐cofactor in studied organisms, suggesting that early Mo‐nitrogenases may have utilized an alternate and/or simplified pathway for cofactor biosynthesis. Our results underscore the profound impacts that protein‐level innovations likely had on shaping global biogeochemical cycles throughout the Precambrian, in contrast to organism‐level innovations that characterize the Phanerozoic Eon.

    more » « less
  5. BACKGROUND Diverse organisms, from archaea and bacteria to plants and humans, use receptor systems to recognize both pathogens and dangerous self-derived or environmentally derived stimuli. These intricate, well-coordinated immune systems, composed of innate and adaptive components, ensure host survival. In the late 20th century, researchers identified the Toll/interleukin-1/resistance gene (TIR) domain as an evolutionarily conserved component of animal and plant innate immune systems. Today, TIR-domain proteins are known to be broadly distributed across the tree of life. The TIR domain was first recognized as an adaptor for the assembly of macromolecular signaling complexes in mammalian innate immune pathways. Work on axon degeneration in animals—as well as on plant, archaeal, and bacterial immune systems—has uncovered additional enzymatic activities for TIR domains. ADVANCES Mammalian axons initiate a self-destruct program upon injury and during disease that is mediated by the sterile alpha and TIR motif containing 1 (SARM1) protein. The SARM1 TIR domain enzymatically consumes the essential metabolic cofactor nicotinamide adenine dinucleotide (NAD + ) to promote axonal death. Identification of the SARM1 NAD + -consuming enzyme (NADase) revealed that TIR domains can function as enzymes. Given the evolutionary conservation of TIR domains, studies investigated whether the SARM1 TIR NADase was also conserved. Indeed, bacteria, archaea, and plant TIR domains possess NADase activity. In prokaryotes, TIR NADase activity is found in an ancient antiphage immune system. In plants, identification of TIR NADase activity and linkage of TIR enzymatic products to downstream signaling components addressed the question of how nucleotide-binding, leucine-rich repeat (NLR) receptors trigger hypersensitive cell death during an immune response. Studies in plants show that their TIR domains can cleave nucleic acids and possess 2′,3′ cyclic adenosine monophosphate (2′,3′-cAMP) and 2′,3′ cyclic guanosine monophosphate (2′,3′-cGMP) synthetase activity that aids cell death programs in plant innate immunity. Thus, TIR domains constitute an ancient family of enzymes that are activated in immune and cell death pathways. OUTLOOK The discovery of TIR-domain enzyme activities carries implications for innate immunity and neurodegeneration. The identification of the SARM1 NADase defined a drug target for a wide number of neurodegenerative diseases that is being exploited in both preclinical and clinical studies. Hyperactive mutations in the SARM1 NADase have been discovered in amyotrophic lateral sclerosis (ALS) patients. Future work will seek to clarify the contribution of the SARM1 axon degeneration pathway to ALS pathogenesis. NAD + biology influences cellular processes from metabolism to DNA repair to aging. How TIR enzymes influence the NAD + metabolome and its associated pathways in bacteria, archaea, plants, and animals will be an exciting area for upcoming investigation. The discovery of the diversity of TIR enzymatic products is revealing signaling pathways across kingdoms. Discovery of TIR enzymatic function in plants and animals may yet inspire studies of enzymatic functions for Toll-like receptors in animals. We anticipate that cross-kingdom studies of TIR-domain function will guide interventions that will span the tree of life, from treating human neurodegenerative disorders and bacterial infections to preventing plant diseases. Conserved TIR-domain enzymatic activity. TIR-domain proteins from prokaryotes and eukaryotes cleave NAD + into nicotinamide (Nam), ADP-ribose (ADPR), cyclic ADP-ribose (cADPR), isomers of cyclic ADP-ribose (2′ or 3′cADPR), and related molecules [e.g., phosphoribosyl adenosine monophosphate (pRib-AMP)]. Plant TIR domains also possess a nuclease activity, can degrade DNA and RNA, and can function as a 2′,3′-cAMP or 2′,3′-cGMP synthetase. TIR enzymatic activity drives cell death and immune pathways across kingdoms. TIR activity can kill cells directly through NAD + depletion or indirectly using enzymatic products as signal molecules. The representative TIR domain structure shown here is Protein Data Bank ID 6O0Q. EDS1, enhanced disease susceptibility 1; ThsA, Thoeris A. 
    more » « less