Crystal Structure of a Mammalian Voltage-Dependent Shaker Family K+ Channel -- Long et al. 309 (5736): 897 -- Science:
Most of our knowledge of Kv channel function comes from studies of the Shaker K+ channel from Drosophila melanogaster and its family members from mammalian cells (2). Shaker family channels have been extensively studied with electrophysiology, because they can easily be expressed in Xenopus laevis oocytes and in other cells. In contrast, nearly all of our knowledge of K+ channel structure is based on studies of prokaryotic K+ channels, because they are more easily expressed at high levels in Escherichia coli. Such studies have taught us much about their pores, selectivity filters, and gates (3).
Eukaryotic Kv channels in many respects are very similar to their prokaryotic counterparts. The selectivity filter sequence is so conserved that we expect its structure to be essentially the same in all K+ channels. The pore's "inverted teepee" arrangement of inner helices, which holds the selectivity filter in its wider half near the extracellular surface, is also expected to be a conserved feature (4). However, beyond their conserved pore and certain domains that regulate the opening of the pore's gate, eukaryotic Kv channels have certain unique features.
Evolutionarily conserved structures with various derived changes? Evolution at work.