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This review is devoted to structural and serological characteristics of the O-antigens (O-polysaccharides) of the lipopolysaccharides of various Proteus species, which provide the basis for classifying Proteus strains to O-serogroups. The antigenic relationships of Proteus strains within and beyond the genus as well as their O-antigen-related bioactivities are also discussed.

Lysine 2-hydroxyisobutyrylation (K hib) is a novel posttranslational modification (PTM), which was thought to play a role in active gene transcription and cellular proliferation. Here we report a comprehensive identification of K hib in Proteus mirabilis (P. mirabilis). By combining affinity enrichment with two-dimensional liquid chromatography and high-resolution mass spectrometry, 4735 2-hydroxyisobutyrylation sites were identified on 1051 proteins in P. mirabilis. These proteins bearing modifications were further characterized in abundance, distribution and functions. The interaction networks and domain architectures of these proteins with high confidence were revealed using bioinformatic tools. Our data demonstrate that many 2-hydroxyisobutyrylated proteins are involved in metabolic pathways, such as purine metabolism, pentose phosphate pathway and glycolysis/gluconeogenesis. The extensive distribution of K hib also indicates that the modification may play important influence to bacterial metabolism. The speculation is further supported by the observation that carbon sources can influence the occurrence of K hib. Furthermore, we demonstrate that 2-hy-droxyisobutyrylation on K343 was a negative regulatory modification on Enolase (ENO) activity, and molecular docking results indicate the regulatory mechanism that K hib may change the binding formation of ENO and its substrate 2-phospho-D-glycerate (2PG) and cause the substrate far from the active sites of enzyme. We hope this first comprehensive analysis of nonhistone K hib in prokaryotes is valuable for further functional investigation of this modification.

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Formation of infectious urinary calculi is the most common complication accompanying urinary tract infections by members of the genus Proteus. The major factor involved in stone formation is the urease produced by these bacteria, which causes local supersaturation and crystallization of magnesium and calcium phosphates as carbonate apatite [Ca 10 (PO 4 ) 6 .CO 3 ] and struvite (MgNH 4 PO 4 .6H 2 O), respectively. This effect may also be enhanced by bacterial polysaccharides. Macromolecules of such kind contain negatively charged residues that are able to bind Ca 2þ and Mg 2þ , leading to the accumulation of these ions around bacterial cells and acceleration of the crystallization process. The levels of Ca 2þ and Mg 2þ ions bound by whole Proteus cells were measured, as well as the chemical nature of isolated LPS polysaccharides, and the intensity of the in vitro crystallization process was compared in a synthetic urine. The results suggest that the sugar composition of Proteus LPS may either enhance or inhibit the crystallization of struvite and apatite, depending on its chemical structure and ability to bind cations. This points to the increased importance of endotoxin in urinary tract infections.