Yet another way of getting more from less
by Don Batten
The Human Genome Project turned up some 30,000 supposed protein-coding genes.1
But protein studies had already suggested that we humans can produce over 100,000
different proteins. As Harrison et al., said, ‘… the human
proteome size is likely to be significantly larger than approximately 90,000.’2
So where do the extra proteins come from?
Known sources of extra variety include:
- DNA editing. This occurs with the production of antibodies in the immune system.
Two mechanisms appear to operate; one involving recombination and the other a targeted
hypermutation of the DNA coding for antibodies.3,4 This incompletely
understood mechanism allows cells in the lymphatic system to quickly generate new
antibodies to deal with pathogens not encountered before. Some apologists for the
evolutionary philosophy have claimed this as an example of information arising from
a random process, but it is irrelevant to biological evolution.5
- Messenger RNA (mRNA) editing. The exon/intron arrangement of genes in eukaryotes
allows for rearrangement of the exons to produce different proteins. For example,
the cSlo gene produces at least 576 different proteins in the hair cells of the
inner ear of chickens.6 These variant proteins are involved in facilitating
hearing by the tuning of the hair cells to different frequencies. Such high levels
of alternative splicing are apparently common in nerve cells.4 Researchers
do not know yet how cells regulate such mRNA editing to generate different proteins.
If each of the 30,000 putative genes produced only four different proteins by mRNA
editing, this would increase the number of possible proteins to 120,000.
Now researchers have found, in humans, a third means of getting more peptides: protein
editing.7 Already known to operate in plants and unicellular organisms,
it also occurs in the production of peptides that label aberrant cells for destruction
by killer T-cells in humans. In a mind-boggling sequence of events, many details
of which still remain obscure, cells recognize foreign (e.g. bacterial) proteins
or wayward self-proteins, such as the excess production of a certain protein in
a cancerous cell, and mark them for destruction. The proteasome8 degrades
the marked proteins into short pieces (oligopeptides). Then a special antigen-processing
transport system moves the pieces to the endoplasmic reticulum where some of the
peptides bind to MHC (Major Histocompatibility Complex ) class 1 molecules. These
complexes are then conveyed to the cell surface, where the MHC molecules present
the peptides, stimulating killer T-cells to destroy the cell.
The researchers found that the peptides presented by the MHC came from a consistent
joining together of the two ends of the aberrant protein—protein editing.
This is the first time this has been shown to occur in vertebrates.
The astonishing complexity of living things never ceases to amaze me. The protein
editing system adds another dimension of complexity to the immune system of vertebrates.
The killer T-cell system appears to be a good example of an irreducibly complex
system. Because the system has to be complete to contribute to fitness, a step-wise
process of small lucky mutations selected by natural selection, per Dawkins, cannot
work. Attributing such incredibly integrated complex systems to chance, the only
alternative to design, defies basic logic.
References
- Batten, D., Catchpoole,
D. and Wieland, C.,
Message Mania: Deciphering the human genome: what does it mean?
Creation 23(3):16–19, June–August
2001.
- Harrison, P.M., Kumar, A., Lang, N., Snyder, M. and Gerstein, M.A., A question of
size: the eukaryotic proteome and the problems in defining it, Nucleic Acids Research
30(5):1083–1090, 2002.
- Shapiro, G.S. and Wysocki, L.J., DNA target motifs of somatic mutagenesis in antibody
genes, Crit. Rev. Immunol. 22(3):183–200, 2002.
- Durandy, A., Activation-induced cytidine deaminase: a dual role in class-switch
recombination and somatic hypermutation, Eur. J. Immunol. 33(8):2069–73,
2003.
- See Truman, R., The unsuitability of B-Cell maturation
as an analogy for neo-Darwinian Theory, <www.trueorigin.org/b_cell_maturation.asp>,
25 May 2004.
- Black, D.L., Minireview: splicing in the inner ear: a familiar tune, but what are
the instruments? Neuron 20:165–168, 1999.
- Hanada, K., Yewdell, J.W. and Yang, J.C., Immune recognition of a human renal cancer
antigen through post-translational protein splicing, Nature 427:252–256,
2004.
- A large protein complex that degrades proteins marked for degradation by various
means.
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