David P. Brunner

Large scale purification and refolding of HIV-1 protease from Escherichia coli inclusion bodies

The protease encoded by the human immunodeficiency virus type 1 (HIV-1) was engineered inEscherichia 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-I 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 ofMr ≈ 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 atpH 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.

Solution structure of human interleukin-1 receptor antagonist protein.

Interleukin‐1 receptor antagonist protein (IRAP) is a naturally occurring inhibitor of the interleukin‐1 receptor. In contrast to IL‐1β IRAP binds to the IL‐1 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‐1 receptor binding are conserved between IRAP and IL‐1β. By contrast, structurally homologous residues critical for receptor activation are not conserved between the two proteins.

Resolution of microheterogeneity associated with recombinant HIV-1 heterodimeric reverse transcriptase.

HIV-1 reverse transcriptase (RT) has been successfully expressed as a biologically active recombinant protein in Escherichia coli and purified to homogeneity. After partial purification, RT was obtained primarily in a heterodimeric form represented by two subunits of 66 and 51 kDa, but the preparation also included several forms distinguishable in size and charge by chromatography on ionic-exchange and gel-filtration columns. We have developed a purification method that yields a single heterodimeric form of RT. Our strategy involves the selection of RT molecules exhibiting uniformity in elution from QAE Sepharose anion-exchange columns and Superose 12 gel-filtration columns. In the former, RT is resolved into multiple peaks on the basis of enzymatic activity, one of which represents highly active and pure p66:p51 heterodimeric RT. This highly active RT fraction, after gel-filtration chromatography, yields a compositionally pure protein product free of observable microheterogeneity by 1D and 2D polyacrylamide gel electrophoresis under a variety of conditions. Furthermore, the RNAse H enzymatic activity associated with HIV-1 RT has been demonstrated to coelute with the purified polymerase activity during gel filtration at a size (120 kDa) consistent with its location on the heterodimeric protein molecule.

Proton, carbon, and nitrogen chemical shifts accurately delineate differences and similarities in secondary structure between the homologous proteins IRAP and IL-1β

Summary1Hα,13Cα, and15Nα secondary chemical shifts, defined as the difference between the observed value and the random coil value, have been calculated for interleukin-1 receptor antagonist protein and interleukin-1β. Averaging of the secondary chemical shifts with those of adjacent residues was used to smooth out local effects and to obtain a correlation dependent on secondary structure. Differences and similarities in the placement of secondary structure elements in the primary segdences of these structurally homologous proteins are manifested in the smoothed secondary chemical shifts of all three types of nuclei. The close correlation observed between the secondary chemical shifts and the previously defined locations of secondary structure, as defined by traditional methods, exemplifies the advantage of chemical shifts to delineate regions of secondary structure.