JTW's Evolutionary Origins - Author: Wachtershauser, Gunter
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Wachtershauser's Elementary Steps of Pathway Evolution
(Granick, 1950)
Elementary Evolutionary Change #1
Terminal Extension:
(---> A --b--> B ) ==> (---> A --b--> B --c--> C ).
"By a change of the chemical environment, the propensity for reaction type c increases and the product B is converted into a product C, thus extending the pathway."
Elementary Evolutionary Change #2
Lateral Branching:
--c--> C
/
(---> A --b--> B ) ==> (---> A --b--> B ).
\
--d--> D )
"All pathway evolution preceeds by these two elementary changes, irrespective of the catalytic involvement of enzymes or (earlier) of metabolically produced pre-enzymatic vitalysts or (still earlier) of environmentally provided catalysts (e.g. metal ions)."
Elementary Evolutionary Change #3
Functional Extension:
FB = FC or FB ~ FC
"The functions of successive constituents B,C may exist in seperate phyla or they may coesxist in the same organism, representing different stages of evolution."
Elementary Evolutionary Change #4
Functional Innovation:
"If a constituent B with a set of functions FB is converted into a constituent C with a set of functions FC,
we have genuine functional innovation,
if FC includes FB but goes beyond FB or, if FB and FC are unrelated."
"The most difficult problem of biochemical phylogeny is concerned with the elucidation of patterns of evolutionary changes, E5 to E11. They frequently change not only the catalyst of a pathway, but also the very constitution of the pathway itself. This problem can be subdivided into the diagnostic problem of identifying those extant pathways that underwent extensive evolutionary changes and the problem of reconstruction of the actual course of pathway evolution."
Elementary Evolutionary Change #5
Functional Takeover:
FB ==> (FB + FC ) ==> FC;
FB~FC
"The structure C may arise by conversion of B or in a pathway not involving B. This notion of a functional takeover has been elaborated by Cairns-Smith for the case of genetic takeover from the vantage point of hypothetical clay organisms."
Elementary Evolutionary Change #6
Pathway Recruitment:
(A ---> B ---> C ---> D )
==>
A ---> B --c--> C --d--> D
!
v
X
==>
A ---> B --c--> C --d--> D
!
v
X ---> B' --c--> C' --d--> D'
"A special case of lateral branching... This can be understood if we recall the importance of the concept of class reactions for biochemical evolution. As soon as a product X of the lateral branching (E2) is converted to B', which is chemically analogous to to B, the pre-existent reaction types c and d will instanly install the parallel pathway form B' to D'. This principle was first extablished by Jensen for enzymatic pathways (enzyme recruitment), but it holds also for pre-enzymatic pathways."
Elementary Evolutionary Change #7
Pathway Abandonment:
(A ---> B ---> C )
==>
A ---> B ---> C
and
A' ---> B' ---> C'
==>
(A' ---> B' ---> C')
"In the evolution of secondary metabolism, the cases of functional takeover concern mainly non-chemical functions. Such takeovers do not obscure the pattern of forward evolution, if they are preserved in a pathway. The pattern of forward evolution is, however, severely obscured if whole pathways are abandoned as a consequence of functional takeover (E5) or pathway recruitment (E6). Such abandonments must have been extensive in the central metabolism."
Elementary Evolutionary Change #8
Pathway Takeover:
(A ---> B )
==>
A --->
B
C --->
==>
(C ---> B )
"The most extensive remodelling of the metabolism occurs by the processes of pathway takeover. This is actually a special case of functional takeover."
Elementary Evolutionary Change #9
Pathway Insertion:
(A ---> B ---> C )
==>
A ---> B ---> C
^
!
D ---> E ---> F
==>
A ---> B ---> C
! ^
v !
D ---> E ---> F
==>
(A ---> D ---> E ---> F ---> C )
"A more complex pattern of pathway evolution occurs by a succession of lateral branching (E2) and pathway takeover (E8). This pattern may turn a short pathway into a long pathway. It occurs frequently and seems to be driven by the benifit of an overall streamlining."
Elementary Evolutionary Change #10
Retrograde mimicry:
(A ---> B ---> C )
==>
A ---> B ---> C
^
!
D ---> E
==>
(D ---> E ---> C )
==>
(D ---> E ---> C )
^
!
F
==>
(F ---> E ---> C )
"The above elements of pathway evolution may be combined in a variety of ways. A most interesting pattern arises by a sequence of pathway takeovers. This evolutionary pattern has the net result that the reactive order of constituents in the final pathway is the reverse of the temporal order of their entry into the pathway. Here, we have a case of retrograde mimicry withing a forward pattern of evolution."
Elementary Evolutionary Change #11
Pathway Reversal:
\ / \ /
v v v v
(A ---> B ---> C ) ==> (A <--- B <--- C )
/ \ / \
v v v v
"Pathways close to chemical equilibrium undergo a reversal, if the chemical conditions change."
"The central pathways in the extant metabolisms have all undergone extensive reconstructuion by the above elementry changes of evolution. One of the most throughgoing patterns of takeover is the takeover of pre-enzymatic pathways by enzymatic pathways. This is actually a case of functional takeover whereby notably the pyrite surface is replaced by the enzyme surface function."
- Wachtershauser, Gunter
- Groundworks for an Evolutionary Biochemistry: The Iron-Sulphur World
- Progress in Biophysics and Molecular Biology: Vol. 58, No. 2, pp.85-202
- 1992
- [Pubmed]
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