Transcript The Major Transitions in Evolution

Metabolic inheritance
Eörs Szathmáry
Collegium Budapest AND Eötvös University
The formose ‘reaction’
formaldehyd
e
autocatalysi
s
glycolaldehyde
Butlerow, 1861
Von Kiedrowski’s replicator
Replication in the formose
reaction
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Replication is non-informational
Autocatalysis – YES
Heredity – NO
Good for metabolism
Not good for genetics
Gánti’s chemoton model (1974)
metabolism
template
copying
membrane
growth
ALL THREE SUBSYSTEMS ARE AUTOCATALYTIC
Is this just logical or also
historical order?
• How much evolution did take place (presumably
on surfaces) before protocells appeared?
The latest edition: OUP 2003
• After several editions
in Hungarian
• Two previous books
(the Principles and
Contra Crick) plus
one essay
• Essays appreciating
the biological and
philosophical
importance
Pathways of supersystem evolution
metabolism
MB
boundary
MT
template
BT
MBT
INFRABIOLOGICAL SYSTEMS
Contemporary autocatalytic
biochemical cycles
• The Calvin cycle (sugar-phosphate making
more sugar-phosphate)
• Reverse citric acid cycle
Primitive ancestry of the reverse
citric acid cycle
• Was proposed by
Günter
Wächtershäuser
(1990)
• Coupled to CO2
fixation and pyrite
formation around
deep-sea hydrothermal
vents
The archaic version
• He even imagined
alternative („mutant”)
cycles
• No experimental
evidence so far
Units of evolution (JMS)
1. multiplication
2. heredity
3. variation
hereditary traits affecting
survival and/or
reproduction
Classification of replicators
Limited
heredity
Holistic
formose
Modular
Von
Kiedrowski
Unlimited
heredity
genes
Limited
(# of individuals)  (# of types)
Unlimited
(# of individuals) << (# of types)
King (1980): evolution of the
coenzymes
• He looked at the metabolic maps then
• Coenzymes looked auto- and cross-catalytic
• BUT the situation is slightly more
complicated
• The idea nicely links to the assumed
primitive ancestry of coenzymes (related to
the idea of the RNA world)
An autocatalytic cycle in the given
environment
Although A is autocatalytic, it is not
strictly needed
Dependent on the environment!
Autocatalysis of the pair (A, B) is
more complicated, but easy to see
If this is big, you may not realize the
autocatalysts
The basic question
• Could one kick-start metabolism just with
external molecules and macromolecules
(genes an enzymes)?
• Influx  buildup of metabolism?
What to do? Work with B. Papp and
Á. Kun
• Use Heinrich’s scope analyis to identify
absolutely essential INTERNAL molecules
• Look for those molecules that yield the
largest increase in metabolic scope
• Stop when there is a functional metabolism
• Check the results with flux balance analysis
(FBA) for the producible compounds in
steady state
Autocatalytic synthesis of CoA in
Synechocysts sp.
• Note: the same cofactor can be autocatalytic in
different ways in different organisms
Metabolic networks
Environmental dependence
• E. coli network under a condition where
only glucose and inorganic compounds
were included in the food set.
• In addition to ATP, NAD, CoA and quinones
were also identified as autocatalytic seeds
under this condition
Conlusions
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Essentially, Gánti and King were right
There IS an autocatalytic seed
At least one coenzyme is always in the seed
BUT the set is environment-dependent
Puts constraints on artifical (re)construction
of (proto)cells
• BIOINFORMATICS HELPS ANSWER
OLD, FUNDAMENTAL QUESTIONS