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Heparin binding by the HIV‐1 tat protein transduction domain

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.