Exploring the role of PilY1 family proteins in natural transformation

The multifunctional Type 4 pili (T4P) are long thin retractile filaments on many bacterial surfaces including the human pathogens Acinetobacter baumannii and Neisseria gonorrhoeae. An important function of some T4P is natural transformation, which is critical for bacterial adaptation and contributes to antibiotic resistance. T4P are homopolymers of the major pilin protein, with a few minor pilins and in some cases a non-pilin protein PilY1, which are thought to cluster at the pilus tip. To better understand natural transformation, I expressed and purified PilY1 from A. baumannii and N. gonorrhoeae. Crystals of A. baumannii PilY1 N-terminal domain were obtained in native and Selenomethioinine-substituted forms that diffract to ~4.5 Å resolution. I showed that purified N. gonorrhoeae PilY1 binds to dsDNA, inhibits natural transformation, and locates at the pilus tip. I propose a mechanism for natural transformation in which DNA wraps around PilY1 and is drawn into the bacterium by pilus retraction.