Structural biology lays the molecular foundation for the modern field of life sciences. In this thesis, X-ray crystallography is the primary resource for atomic detail structural information and is the major technology employed in our research. Three examples show how structural biology addresses the basic processes of life. Firstly, two crystal structures of R21, corresponding to two biological states, reveal a new activation mechanism of SAR-endolysin, which not only complements the previous model, but is also more generally applicable to the endolysin family. The structural information was further corroborated by NMR data in solution. The second example is the crystal structure of mycobacteriophage lysin B, which identified the function of the protein, and tackles the unique problem of how mycobacteriophage circumvent the mycolic acid-rich outer membrane of mycobacterium. The last example is the homology modeling of the Plasmodium ribosomal L4 protein. The action mode for the drug in Plasmodium was proposed based on that, which accounts for the anti-malaria effect of azithromycin.