The Ancestor of P-type ATPases?
One of the open reading frames in the genome of Methanococcus jannaschii deserves special attention, because it might reveal information about the evolution of the ancestor P-type ATPase.
The open reading frame - MJ0968 (Q58378) - encodes a protein of 273 amino acids that when expressed in E. coli is capable of hydrolysing ATP, is autophosphorylated and is inhibited by orthovanadate (Ogawa. H. et al. (2000) FEBS Lett. 471: 99-102). The sequence aligns with type I ATPases, the highest identities being 30% (over 259 amino acids) to the CopA protein (O08462) of Helicobacter pylori (a type IB ATPase) and 25% (over 235 amino acids) to the KdpB protein (P03960) of Escherichia coli (a type IA ATPase). The sequence has been included in the alignment of type IB P-type ATPases.
Phylogenetic analysis of the conserved segments e, f, g and h of MJ0968 protein together with type I ATPases shows that MJ0968 protein is most closely related to type IB ATPases, even though it is very diverged.
MJ0968 protein covers the big cytoplasmic loop common to all P-type ATPases, which contain all the amino acids involved in ATP binding and hydrolysis. The N-terminal of MJ0968 is positioned 15 amino acids into the universally conserved segment e, 7 amino acids before the phosphorylated aspartate, which is part of the P-type ATPase fingerprint DKTGTLT. This fingerprint is partly conserved in MJ0968 as DSAGTLV. The other amino acids involved in ATP hydrolysis in P-type ATPases can also be found in MJ0968 (for details see Aravind, L., et al. (1998) Trends Biochem. Sci. 23: 127-129).
The current suggestion is that this soluble protein has fused with one or several different ion channels thus forming one or several different types of P-type ATPases, the first probably being a type IB P-type ATPase.
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