ABSTRACT
Bacterial microcompartments are large supramolecular assemblies, resembling viruses in size and shape, found inside many bacterial cells. A protein-based shell encapsulates a series of sequentially acting enzymes in order to sequester certain sensitive metabolic processes within the cell. Crystal structures of the individual shell proteins have revealed details about how they self-assemble and how pores through their centers facilitate molecular transport into and out of the microcompartments. Biochemical and genetic studies have shown that enzymes are directed to the interior in some cases by special targeting sequences in their termini. Together, these findings open up prospects for engineering bacterial microcompartments with novel functionalities for applications ranging from metabolic engineering to targeted drug delivery.
Subject(s)
Bacteria/cytology , Bacterial Proteins/chemistry , Bacterial Proteins/metabolism , Bioengineering/methods , Cell Compartmentation , Bacteria/metabolism , Bacteria/ultrastructure , Metabolic Engineering , Models, MolecularABSTRACT
The lymphoid tyrosine phosphatase (LYP), encoded by the PTPN22 gene, recently emerged as an important risk factor and drug target for human autoimmunity. Here we solved the structure of the catalytic domain of LYP, which revealed noticeable differences with previously published structures. The active center with a semi-closed conformation binds a phosphate ion, which may represent an intermediate conformation after dephosphorylation of the substrate but before release of the phosphate product. The structure also revealed an unusual disulfide bond formed between the catalytic Cys and one of the two Cys residues nearby, which is not observed in previously determined structures. Our structural and mutagenesis data suggest that the disulfide bond may play a role in protecting the enzyme from irreversible oxidation. Surprisingly, we found that the two noncatalytic Cys around the active center exert an opposite yin-yang regulation on the catalytic Cys activity. These detailed structural and functional characterizations have provided new insights into autoregulatory mechanisms of LYP function.
Subject(s)
Catalytic Domain , Intracellular Signaling Peptides and Proteins/chemistry , Intracellular Signaling Peptides and Proteins/metabolism , Amino Acid Sequence , Catalytic Domain/genetics , Crystallization , Crystallography, X-Ray , Cysteine/chemistry , Cysteine/genetics , Cysteine/metabolism , Disulfides/chemistry , Homeostasis/genetics , Humans , Hydrogen Bonding , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/physiology , Molecular Sequence Data , Multigene Family , Oxidation-Reduction , Phosphates/metabolism , Signaling Lymphocytic Activation Molecule Associated ProteinABSTRACT
A gain-of-function R620W polymorphism in the PTPN22 gene, encoding the lymphoid tyrosine phosphatase LYP, has recently emerged as an important risk factor for human autoimmunity. Here we report that another missense substitution (R263Q) within the catalytic domain of LYP leads to reduced phosphatase activity. High-resolution structural analysis revealed the molecular basis for this loss of function. Furthermore, the Q263 variant conferred protection against human systemic lupus erythematosus, reinforcing the proposal that inhibition of LYP activity could be beneficial in human autoimmunity.