Heparin binding by the HIV-1 tat protein transduction domain

Abstract

The protein transduction domain from the HIV-1 tat protein (termed PTD-tat) has been fused to the C-terminus of a model cargo protein, the IgG binding domain of streptococcal protein G. We demonstrate that PG-Ctat (PTD-tat fused to the C-terminus of protein G) binds to a heparin affinity column. PG-Ctat binds with relatively high affinity, as shown by its elution at 1.6 M NaCl. The heparin binding properties of PTD-tat are consistent with the idea that heparan sulfate, an analog of heparin found at the cell surface, plays a role in the translocation of PTD-tat fusions. We suggest that the heparin-binding properties of PTD-tat can be exploited for purification of PTD-tat fusions in the absence of affinity tags.

Fig. 1.

Chromatograms of PG (dashed line) and PG-Ctat (solid line) binding to a heparin affinity column. The flow rate was set to 5 mL/min. The injection volume was 50 μL. The elution conditions were 8 min of 20 mM Tris-HCl/pH 8.0, 150 mM NaCl followed by 20 mM Tris-HCl/pH 8.0 and a 150 mM to 2000 mM NaCl gradient over 8 min. The percentage of elution buffer is shown as a dotted line.