Adenosine Kinase, Cyclin-Dependent Kinase 2, and HIV-1 Integrase are all integrases (or have domains that have integrase activity). While none are homologous to any of the others, they do share some similarities:

1) All are proteins that contain both alpha-helices and beta-sheets

2) All have a metal ion that is bound in the active site to aid the catalyzed reaction

3) All can be found in the cytoplasm of cells

Each protein listed in the website has similarities but there are also differences. CDK2 has many different targets and plays a crucial role in regulation of the cell cycle, Adenosine Kinase has an important role in engery production and regulation, and HIV-1 Integrase is important in the replication cycle of the HIV-1 virus. While on first glance these protiens seem small and unimportant they are actually essential to cell survival and must be present for organisms to functions.