The present invention relates to human Janus Kinase 3 (JAK3) and JAK3-like binding pockets. The present invention provides a computer comprising a data storage medium encoded with the structure coordinates of such binding pockets. This invention also relates to methods of using the structure coordinates to solve the structure of homologous proteins or protein complexes. In addition, this invention relates to methods of using the structure coordinates to screen for and design compounds, including inhibitory compounds, that bind to JAK3 protein or JAK3 protein homologues, or complexes thereof. The invention also relates to crystallizable compositions and crystals comprising JAK3 kinase domain and JAK3 kinase domain complexed with AMP-PNP.