To cite package ‘protr’ in publications use:

  Xiao N, Cao D, Zhu M, Xu Q (2015). “protr/ProtrWeb: R package and web
  server for generating various numerical representation schemes of
  protein sequences.” _Bioinformatics_, *31*(11), 1857-1859.
  doi:10.1093/bioinformatics/btv042
  <https://doi.org/10.1093/bioinformatics/btv042>.

A BibTeX entry for LaTeX users is

  @Article{xiao2015protr,
    title = {protr/{ProtrWeb}: {R} package and web server for generating various numerical representation schemes of protein sequences},
    author = {Nan Xiao and Dong-Sheng Cao and Min-Feng Zhu and Qing-Song Xu},
    journal = {Bioinformatics},
    volume = {31},
    number = {11},
    pages = {1857--1859},
    year = {2015},
    doi = {10.1093/bioinformatics/btv042},
  }