Analysis of recombinant human interleukin-11 fusion protein derived from Escherichia coli lysate by combined size-exclusion and reversed-phase liquid chromatography

A two-dimensional size-exclusion-reversed-phase high-performance liquid chromatographic assay has been developed for the quantitation of recombinant human interleukin-11 fusion protein (rhIL-11 FP) expressed in E. coli cells. The sample preparation procedure included the optimization of lysis buffer components to achieve maximum rhIL-11 FP recovery through the disruption of associations between rhIL-11 FP and E. coli components. The E. coli cells were dialyzed into lysis buffer and lysed by a French Press prior to two-dimensional chromatographic analysis. A size-exclusion column was used first to remove high- and low-molecular-mass E. coli components. Then reversed-phase chromatography was used to separate and quantify the rhIL-11 FP. The assay was linear over the range of 0.0294 to 0.235 mg/ml. The limit of quantitation, 0.0294 mg/ml, was based on % normalized residuals and precision criteria not exceeding 10%. The reproducibility of the assay for lysate samples was good on a daily (% R.S.D.=1.0; n=5) and a day-to-day (% R.S.D.=3.2; n=10) basis. The assay was also monitored by an external control, in which day-to-day reproducibility was good (% R.S.D.=2.2; n=9). Selectivity and chromatographic peak identification were based upon gel electrophoresis and N-terminal sequencing of the rhIL-11 FP peak collected from the reversed-phase column.