Jeannie R. Rojas

The yeast GCN5 (yGCN5) transcriptional coactivator functions as a histone acetyltransferase (HAT) to promote transcriptional activation. Here, we present the high resolution crystal structure of the HAT domain of yGCN5 and probe the functional importance of a conserved glutamate residue. The structure reveals a central protein core associated with AcCoA binding that appears to be structurally conserved among a superfamily of N-acetyltransferases, including yeast histone acetyltransferase 1 and Serratia marcescens aminoglycoside 3-N-acetyltransferase. A pronounced cleft lying above this core, and flanked by N- and C-terminal regions that show no sequence conservation within N-acetyltransferase enzymes, is implicated by cross-species conservation and mutagenesis studies to be a site for histone substrate binding and catalysis. Located at the bottom of this cleft is a conserved glutamate residue (E173) that is in position to play an important catalytic role in histone acetylation. Functional analysis of an E173Q mutant yGCN5 protein implicates glutamate 173 to function as a general base for catalysis. Together, a correlation of the yGCN5 structure with functionally debilitating yGCN5 mutations provides a paradigm for understanding the structure/function relationships of the growing number of transcriptional regulators that function as histone acetyltransferase enzymes.

OBJECTIVE: To assess the effect of golimumab (human monoclonal antibody to tumor necrosis factor-alpha) plus methotrexate (MTX) on selected inflammatory biomarkers, and to determine if these effects predict clinical response in rheumatoid arthritis (RA). METHODS: Sera from adults with active RA despite MTX therapy, who received subcutaneous injections of placebo + MTX (MTX alone, n = 34) or golimumab 50 or 100 mg every 2 or 4 weeks + MTX (n = 137), were analyzed for levels of C-reactive protein (CRP), serum amyloid A (SAA), interleukin 18 (IL-18), E-selectin, matrix metalloproteinase 9 (MMP-9), and tissue inhibitor of matrix metalloproteinase 1 (TIMP-1). RESULTS: Golimumab + MTX treatment significantly decreased serum CRP, SAA, IL-18, E-selectin, TIMP-1, and MMP-9 levels (median percent changes of -4.1% to -74.3% across treatment groups) versus MTX alone (-5.8% to 9.7%) when first measured at Week 4; decreases were sustained through Week 16. Larger magnitudes of decrease in all biomarkers were observed for clinical responders versus nonresponders. For golimumab + MTX, regression analyses including all biomarkers and select clinical measures showed that reductions in levels of several markers (SAA, E-selectin, MMP-9) as early as Week 4 correlated significantly with improvement in swollen joint count (SJC) at Week 16, as did reductions in E-selectin with improvement in tender joint count at Week 16. After accounting for the biomarkers, however, treatment group was no longer significant for SJC. CONCLUSION: Significant decreases in several inflammatory biomarkers were associated with golimumab + MTX therapy. Decreases in serum levels of SAA, E-selectin, and MMP-9 at Week 4 may be useful in predicting clinical response at Week 16.