Site 1 (click me) 

HILL is a web application that indexes helical parameters (pitch/twist, rise, and csym) based on Fourier space layer line amplitudes and phases. A protein helix is modeled as a continuous helix multiplied by a set of parallel, equally spaced planes that are repeated along the helical axis. According to the convolution theorem, the Fourier transform of a protein helix is the convolution of the Fourier transform of the continuous helix, which has an X-like pattern of equally spaced layer planes/lines centered at the Fourier origin with a spacing equal to 1/pitch, and Bessel functions of increasing orders describing the amplitude radial profile of each of the layer planes/lines, and the Fourier transform of the parallel planes, which is a set of equally spaced points along the helical axis with the spacing equal to 1/rise and with rise equal to the spacing between the parallel planes. In simpler terms, the convolution in Fourier space duplicates the X-pattern of the layer planes/lines at the Fourier origin to each of the points at n/rise (n=0, ±1, ±2, …) along the axis.

The HILL web app provides an intuitive graphical user interface that allows users to manually adjust the pitch and rise values to match the predicted layer line pattern with the layer line pattern in the Fourier transform of a cryo-EM image of the protein helix (typically from a good 2D class average of the helical segments).

No software installation is required. Simply click on one of the available sites to index your structure. 

Citation

A manuscript in under preparation.