Methicillin-resistant Staphylococcus aureus strains produce a fifth penicillin-binding protein (PBP), PBP 2', with low affinity for I-lactam antibiotics that is believed to represent a P-lactam-insensitive peptidoglycan transpeptidase. In an effort to evaluate the adequacy of PBP 2' as an explanation of methicillin resistance, PBP 2' production and the responses of growth and peptidoglycan synthesis to methicillin under different environmental conditions have been compared. In the heterogeneous methicillin-resistant strain DU4916-K7, less PBP 2' was produced at 40°C than at 30°C, but inclusion of 5% (wt/vol) NaCl in the medium at 40°C boosted PBP 2' production and allowed growth of the organism in the presence of 10 ,ug of methicillin per ml. When exponential-phase cultures were challenged with methicillin, growth and peptidoglycan synthesis were much more resistant at 30°C than at 40°C. Inclusion of NaCl in medium rendered growth and peptidoglycan synthesis more methicillin resistant at 40°C. Hence, there was a good correlation between PBP 2' production and methicillin-resistant peptidoglycan synthesis under these conditions. However, PBP 2' production was increased by NaCI at 30°C without markedly affecting the susceptibilities of growth and peptidoglycan synthesis to methicillin. Pregrowth of cells with methicillin, which was expected to boost PBP 2' production, seemed to increase the susceptibilities of growth and peptidoglycan synthesis to methicillin. Patterns of growth and peptidoglycan synthesis susceptibilities to methicillin which were similar to those described above were found in chloramphenicol-inhibited cultures, in which presumably no induction of PBP 2' could occur during the methicillin challenge period. Complex effects were noted in the combination of subinhibitory methicillin and NaCl. Growth of cells in the presence of NaCl stimulated their autolytic activity, which was further increased by growth with subinhibitory methicillin in addition to NaCl. It appears that NaCl enhances methicillin resistance by stimulating PBP 2' production and providing osmotic support but opposes it by stimulating autolytic activity which is exacerbated by the very low cross-linking of peptidoglycan in methicillin-resistant strains grown in the presence of methicillin.

The protease encoded by the human immunodeficiency virus type 1 (HIV-1) was engineered in Escherichia coli as a construct in which the natural 99-residue polypeptide was preceded by an NH2-terminal methionine initiator. Inclusion bodies harboring the recombinant HIV-1 protease were dissolved in 50% acetic acid and the solution was subjected to gel filtration on a column of Sephadex G-75. The protein, eluted in the second of two peaks, migrated in SDS-PAGE as a single sharp band of M(r) approximately 10,000. The purified HIV-1 protease was refolded into an active enzyme by diluting a solution of the protein in 50% acetic acid with 25 volumes of buffer at pH 5.5. This method of purification, which has also been applied to the purification of HIV-2 protease, provides a single-step procedure to produce 100 mg quantities of fully active enzyme.

Interleukin-1 (IL-1) proteins, such as IL-1 beta, play a key role in immune and inflammatory responses. Interaction of these cytokines with the IL-1 receptor induces a variety of biological changes in neurologic, metabolic, hematologic, and endocrinologic systems. Interleukin-1 receptor antagonist protein (IRAP) is a naturally occurring inhibitor of the interleukin-1 receptor. The 153-residue protein binds to the receptor with an affinity similar to that of IL-1 beta but does not elicit any physiological responses. As a first step toward understanding IRAP's mode of action, we have used multidimensional, heteronuclear NMR spectroscopy to determine the antagonist's solution secondary structure and global fold. Using a combination of 3D 1H-15N NOESY-HMQC and TOCSY-HMQC and 3D 1H-15N-13C HNCA and HN(CO)CA experiments on uniformly 15N- or doubly 13C/15N-enriched IRAP, we have made resonance assignments for more than 90% of the main-chain atoms. Analysis of short- and long-range NOE's indicates that IRAP is predominantly beta-sheet, with the same overall topology as IL-1 beta but with different regions of the primary sequence comprising the beta-strands. Two short helical segments also were identified. The 14% sequence identity between IL-1 beta and IRAP increases to 25% when differences in the locations of secondary structure elements in the primary sequences are taken into account. Still, numerous differences in side chains, which ultimately play a major role in receptor interaction, exist.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract. An active recombinant preparation of the carboxy-terminal ribonuclease H (RNase H) domain of HIV-I reverse transcriptase has produced crystals of several different forms, including a trigonal prism form (P31; a = b = 52.03, c = 113.9 /k with two molecules per asymmetric unit) and a hexagonal tablet form (P6222 or P6422; a = b = 93.5, c = 74

We engineered a prokaryotic expression vector encoding the HIV reverse transcriptase (RT). We grew Escherichia coli JM109 carrying the vector in a 250-liter stirred tank fermentor and purified RT (p66) under native conditions to apparent homogeneity. Purified p66 (greater than or equal to 5 mg/ml) was not stable, and was rapidly processed to its 51 kD derivative (p51), until p66:p51 levels were approximately 1:1. These latter RT preparations were chromatographed as heterodimers and had approximately fivefold higher specific RT enzymatic activities compared with those containing predominantly p66. P66 purified under dilute concentrations (less than or equal to 0.5 mg/ml) was monomeric in solution, resistant to p51 processing for weeks at 4 degrees C, but also had low specific RT enzymatic activities. To attempt the preparation of homogeneous p66 with specific RT enzymatic activities equivalent to p66:p51 heterodimers, purified heterodimers were denatured and p66 was purified and refolded during extensive dialysis (refolded p66). Refolded p66 (less than or equal to 0.5 mg/ml) was monomeric in solution and had identical specific RT enzymatic activities, Km for dTTP, and inhibition by 3'-azido-3'-deoxythymidine triphosphate compared with heterodimeric p66:p51 RT. The data indicates that HIV RT obtained from recombinant E. coli under native conditions is extensively processed at concentrations promoting dimerization. Moreover, RT denaturation and refolding yields apparently homogeneous monomeric p66, with specific RT enzymatic activities equivalent to heterodimeric RT.

Interleukin-1 receptor antagonist protein (IRAP) is a naturally occurring inhibitor of the interleukin-1 receptor. In contrast to IL-lb, IRAP binds to the IL-l receptor but does not elicit a physiological response. We have determined the solution structure of IRAP using NMR spectroscopy. While the overall topology of the two 153-residue proteins is quite similar, functionally critical differences exist concerning the residues of the linear amino acid sequence that constitute structurally homologous regions in the two proteins. Structurally homologous residues important for IL-l receptor binding are conserved between IRAP and IL-l/!?. By contrast, structurally homologous residues critical for receptor activation are not conserved between the two proteins.

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