Protein sequence space is vast compared to protein fold space. This raises important
questions about how structures adapt to evolutionary changes in protein sequences. A
growing trend is to regard protein fold space as a continuum rather than a series of discrete
structures. From this perspective, homologous protein structures within the same functional
classification should reveal a constant rate of structural drift relative to sequence changes.
The clusters of orthologous groups (COG) classification system was used to annotate …