Below is the complete text of a presentation given at the Conference on the
Structure and Model of the First Cell, held in Trieste, Italy, between Agust
and September of 1994. It was subsequently published in both the _Journal of
Biological Physics_ and in the conference proceedings, _Chemical Evolution:
Structure and Model of the First Cell_, Kluwer Academic Publishers,
Dordrecht, Netherlands, 1995. This paper not only claims that proteinoid
microsphere protocellss are alive, it also proposes a new taxonomic catagory
to contain all the morphological variations of this kind of protocell. Even
though the conference was attended by people who do not accept the proteinoid
microsphere model for the protocell, as far as I have been able to determine
the paper was well received and its conclusions were not challenged; at least
no one published any papers refuting them. The paper also briefly discusses
that certain types of proteinoid microsphere protocells -- called
metaprotocells -- have been demonstrated to convert light into ATP, to use
that ATP to make polynucleotides, and then to use those polynucleotides as
templates to make polypeptides. In essence then metaprotocells provide the
link between simple chemicals and the RNA world scenario, as well as
demonstrate that proteinoid microspheres could have evolved the modern
genetic coding system on their own.
I should also point out that, from reading the conference proceedings, even
as late as 1994 no one had still been able to duplicate what Fox and others
have done and create a non-proteinoid microsphere protocell in the lab. Nor
do any of the other papers provide any experimental continuity between simple
chemicals and protocells, or any experimental evidence showing how that
protocell model could have evolved into a model cell. There was a lot of
speculation, but except for the proteinoid microsphere model papers precious
little hard evidence.
=========================
Journal of Biological Physics 20: 129-132, 1994.
c 1995 Kluwer Academic Publishers. Printed in the Netherlands.
DOMAIN PROTOLIFE
Protocells and metaprotocells within thermal protein matrices
ARISTOTEL PAPPELIS
Department of Plant Biology, Southern Illinois University at Carbondale,
Carbondale, Illinois 62901 U.S.A.
SIDNEY W. FOX
Coastal Research and Development Institute, University of South Alabama,
Mobile, Alabama 36688 U.S.A.
Abstract. We propose the Thermal Protein First Paradigm (protocell theory)
that affirms that first life was cellular. The first cells emerged from
molecular (chemical) evolution as protocells (heated amino acids self-order
in copolymerization reactions to form thermal proteins which self-organize
when in contact with water to form protocells). Metaprotocells are
specialized protocells capable of synthesizing ATP (light energy conversion
to chemical energy), polypeptides, and polynucleotides. Aggregations of
protocells in thermal protein matrices form distinctive morphologies
(protocellular networks). Prokaryotic cells emerged from metaprotocells. We
classify protocells and metaprotocells as members of the Domain Protolife. We
revised the cell theory to include protolife.
1. Introduction
In May of 1994, we presented the Thermal Protein First Paradigm that
described the emergence of cellular life to scientists gathered in the A. N.
Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia
for the purpose of celebrating the Centennial Anniversary of Academician
Alexander Ivanovich Oparin. His contributions that linked the concept of
chemical evolution to the origin of life were reviewed. Oparin's experiments
with coacervate droplets were not successful in synthesizing cellular life.
Success in synthesizing protocellular life was achieved by Fox and associates
[1] using the homoacervate model with thermal proteins. We described those
successful studies and proposed that the synthesis of cellular life had been
achieved without being appreciated as such in the late 1950's and early
1960's. Realization of the significance of the synthesis of protocells
occurred in the late 1970's and early 1980's after many studies of the
attributes of life exhibited by them had been reported, especially their
abilities to synthesize ATP, polypeptides, and polynucleotides.
In the 1990's, we discovered aggregations of protocells in thermal protein
matrices (protocellular networks). These formed distinctive morphologies
determined by the amino acid composition of the thermal proteins used in the
synthesis of protocells. The Thermal Protein First Paradigm describes the
link between Oparin's proposal (life originated from chemical substances) and
biological evolution (concepts developed over the past 140 years; DNA-based
genetic determinism).
The impact of the synthesis of protocells on biological classification was
discussed by us in several courses and in various presentations at
professional meetings. We proposed that protolife, as discovered in the
laboratory by synthesis [1, 2] accounted for the emergence and evolution of
life and should be classified as a new taxonomic group called Domain
Protolife. We preferred that term because it could be linked to the natural
system of organisms described by Woese et al. [3]. From protocells could be
selected complex types in which ATP synthesis, nonribosomal polypeptide
synthesis, polynucleotide synthesis, and signal transduction would occur. We
used the term metaprotocells to describe this advanced form of specialized
protolife from which prokaryotic organisms could emerge. The term Kingdom
Protolife [4] could be employed by biologists using more traditional
classification systems [5].
The emergence of cellular life from evolving carbon compounds is described by
the Thermal Protein First Paradigm. Evidence supporting our proposal [6, 7,
8, 9, 10, 11] has been reviewed elsewhere in this volume (Fox et al.) and
summarized by Fox and Pappelis [2]. We equate the metaprotocells with
progenotes [12, 13]. Metaprotocells are expected to be in various stages of
evolution in which a translation apparatus linking genotype and phenotype has
not yet achieved the state observed in modem cells. Prokaryotic cells emerged
from these metaprotocells. Eukaryotic cells emerged from a prokaryotic
ancestor at a later time [3]. Thus, our proposal establishes continuity and
direction within a cosmogenic system (energy being converted to subatomic
particles; subatomic particles forming atomic nuclei and elements; galactic
clouds forming galaxies; supernovae forming heavy elements; solar systems
forming from star dust around a second generation star such as our sun;
carbon compounds emerging as part of chemical evolution; protolife emerging
on Earth and evolving to prokaryotic cells; and, eukaryotic cells emerging
from prokaryotic ancestors of several types with endosymbionts that account
for mitochondrial and chloroplast genomes).
2. Thermal Protein First Paradigm
We were able to describe the emergence and evolution of life as follows:
life as we know it (Domains Archea, Bacteria, and Eucarya) evolved from life
as we don't quite know it (Domain Protolife). We summarized the process as
follows:
a. Carbon chemistry yields substrates for the synthesis of thermal proteins
in reactions involving terrestrial heat (endogenously self-ordered, highly
nonrandom polyamino acids; anhydrocopolymerization).
b. In contact with water, thermal proteins yield a matrix in which
protocells (proteinoid microspheres) arise by self-organization
(self-assembly) reactions (three-dimensional phase transitions;
self-chaperoned; surface chemistry phenomena yielding a double membrane
boundary). The protocells encapsulate (microencapsulation) non-organized
thermal proteins (protocytoplasm). We visualize the anionic-cationic nature
of amino acids cause them to be aggregated by each other, with strong
modulation by the side chains. The same forces in polymer form are active in
cellular assemblies. The morphologies of these assemblies are affected in
addition by polyionic matrices. A common basis and mode of organization is
thus seen for all levels of evolution. How much is contributed at each level
is the subject for future research.
c. Protocells exhibit the attributes of cellular life (except DNA-based
genetics). They are the smallest units of protolife. They may exist as
individual protocells or as linked multiprotocellular structures.
d. Protocells that transform light energy into chemical energy (synthesis of
ATP), conduct nonribosomal polypeptide synthesis, and synthesize
polynucleotides (within the double membrane boundary) are defined to be
metaprotocells. Metaprotocells that retain proteins and evolving
polynucleotides in the protocytoplasm are the units of protolife from which
prokaryotic cells emerge (the most recent common ancestor of prokaryotic
cells).
e. The Domain Protolife is proposed to show the relatedness of all life
forms emerging in an understandable sequence: continuity with chemical
evolution in the expanding universe (molecular determinism); and,
directionality on earth ("informed" thermal proteins synthesizing stable and
mutating "informed" polynucleotides which, with protein catalysts, enable the
emergence of DNA-based genetic determinism).
Our proposal of the Thermal Protein First Paradigm can be best understood as
an extension of an earlier summarization [14] describing molecular and
natural selection:
a. Evolution is viewed as being cosmological in scope.
b. "Molecular selection" is as natural as "natural selection" (the former
taking precedence over the later).
c. "Molecular selection" is primarily endogenous for a living organism,
whereas "natural selection" in exogenous.
d. "Molecular selection" occurred in the thermal protein matrices from which
life emerged (direct emergence of a stable and dynamic protocell; molecular
and biological evolution results in the emergence of prokaryotic cell).
e. Artificial fossils of protolife are indistinguishable from many ancient
microfossils.
Thus, we believe that the first terrestrial cells are like those obtained in
laboratory experiments. We believe that extraterrestrial life would emerge
through protocells like those described in Domain Protolife. We describe the
new taxonomic group we call Domain Protolife as follows: protocells and
metaprotocells (neither prokaryotic nor eukaryotic); porous protocellular
membranes of thermal protein (seen as two closely associated membranes using
transmission electron microscopy) with lipid attributes (retaining small
macromolecules within the protocellular boundary). ATP synthesis
(transformation of light energy into chemical energy), nonribosomal
polypeptide and protein synthesis, and polynucleotide and nucleic acid
synthesis in metaprotocells (ribosomes absent). Advanced metaprotocells
contain an RNA-directed (replicating) genome and have the capability to
evolve DNA-directed inheritance (genetic determinism). Protospecies have
distinctive morphologies formed by external thermal protein matrices and
aggregated protocells they envelope (protocellular networks).
We place great significance on the use of synthetic methods and the role of
evolutionary continuity and directionality in discovering protolife. We
believe that molecular phylogeny in the Domain Protolife will be discovered
in the amino acid sequences of thermal and nonthermal proteins contained in
protocells, metaprotocells, arid prokaryotic cells. We propose that it is
appropriate to begin intensive analytical studies of the activities of
protocells and metaprotocells that lead to the display of the attributes of
life. The basis of biological diversity is in molecular structures that are
present in protocellular networks. Study of the structure and function of the
protocellular networks is now appropriate. Protocellular networks converted
to artificial microfossils may prove helpful to those seeking fossil evidence
of early terrestrial and extraterrestrial protolife by using the methods of
comparative morphology.
References
1. S. W. Fox, The Emergence of Life, Darwinian Evolution From the Inside,
New York: Basic Books, 1988.
2. S. W. Fox and A. Pappelis, "Synthetic molecular evolution and
protocells," Quarterly Review of Biology, Vol. 68, 1993, pp. 79-82.
3. C. R. Woese, O. Kandler, and M. Wheelis, "Toward a natural system of
organisms: Proposal for Domain Archaea, Bacteria, and Eucarya," Proceedings
of the National Academy of Science USA, Vol. 87, 1990, pp. 4576-4579.
4. A. Pappelis, S. W. Fox, and M. D. Papagiannis, "Protocells and
metaprotocells of the Protolife Kingdom," Transactions of the Illinois State
Academy of Science, Vol. 86 (Supplement), p. 57 (Abstract).
5. J. O. Corliss, "Protistan phylogeny and eukaryogenesis," International
Review of Cytology, Vol. 100, 1987, pp. 319-370.
6. O. C. Ivanov and B. Frtsch, "Universal regularities in protein primary
structure: preferences in bonding and periodicity," Origins of Life and
Evolution of the Biosphere, Vol. 17, 1986, pp. 35-49.
7. O. C. Ivanov, "Some proteins keep 'living fossil' pre-sequence," Origins
of Life and Evolution of the Biosphere, Vol. 23, 1993, pp. 115-124.
8. S. Tyagi and C. Ponnamperuma, "Nonrandomness in prebiotic peptide
synthesis," Journal of Molecular Evolution, Vol. 30, 1990, pp. 391-399.
9. P. Melius and C. Srisomsap, "Nonrandom thermal polymerization of amino
acids," Journal of Applied Polymer Science, Vol. 42, 1991, pp. 1167-1168.
10. A. Bar-Nun, E. Kochavi, and S. Bar-Nun, "Assemblies of free amino acids
as possible prebiotic catalysts," Journal of Molecular Evolution, Vol. 39,
1994, pp. 116-122.
11. O. Davydov, "The reverse genetic code and the Central Dogma of molecular
biology," Origins of Life and Evolution of the Biosphere, Vol. 24, 1994, p.
216 (Abstract).
12. C. R. Woese, "Evolutionary questions: The 'Progenote'," Science, Vol.
247, 1990, p. 789.
13. C. R. Woese and G. E. Fox, "The concepts of cellular evolution," Journal
of Molecular Evolution, Vol. 10, 1977, pp. 1-6.
14. S. W. Fox, "Molecular selection and natural selection," Quarterly Review
of Biology, Vol. 61, 1986, pp. 375-386.
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Kevin L. O'Brien