Purification and Properties of the Colicin E3 Receptor of ITscherichia coZi*

Colicin E3 receptor activity was extracted from the envelope fraction of colicin-sensitive Escherichia coli cells with Triton X-100 and EDTA, and was purified by ion exchange chromatography on DEAE-cellulose. The purified receptor fraction retained full receptor activity against both colicin E2 and E3, but it had little activity towards colicin El and almost no colicin K receptor activity. A protein with a molecular weight of about 60,000 was detected in purified fractions by polyacrylamide gel electrophoresis. During the final stages of purification this protein was enriched in proportion to the specific activity of the colicin receptor. When excess colicin E3 was added to the purified receptor fraction and then precipitated with rabbit anticolicin, this 60,000 molecular weight protein was co-precipitated with the colicin, whereas other contaminating protein was only partially precipitated. In order to further confirm the relationship between this protein and colicin receptor activity, a culture of a colicin-sensitive strain was labeled with 3H-amino acids and mixed with a culture of a colicin-resistant mutant strain labeled with 14C-amino acids. When the purified receptor fraction obtained from this mixed culture was analyzed by gel electrophoresis, it was observed that the 60,000 molecular weight protein was labeled only with 3H, indicating that this protein is missing or altered in the colicin-resistant mutant. It was estimated that there are 220 copies of this protein per cell. The purified receptor activity was inactivated by periodate, suggesting that a carbohydrate is also required for activity. A small amount of carbohydrate was present in the purified receptor fraction, and preliminary analysis indicated that glucose, galactose (and/or heptose), rhamnose, uranic acids, and amino sugars were present. The 60,000 molecular weight protein did not appear to contain any large amount of covalently linked carbohydrate. As yet, there is no evidence to confirm the identity of any specific carbohydrate which is essential for receptor activity.