Some bacteria use "secretion systems" (SS) to do various things: they help humans digest food, they are capable of horizontal gene transfer, and some use them to inject toxins into their victims. There are different types, and I had described two of them, Type II SS and IV, in a previous post HERE. Since the beginning of gene sequencing in the 1990s, scientists are becoming aware that not all genes are following the expected Darwinian tree. So they used horizontal gene transfer as their explanation: some genes went to different species under different conditions than the strict mutation and natural selection model that Darwin proposed. I also discussed that in the post mentioned above.
But the Type III secretion system (T3SS) itself has been used as a possible structure that could be a Darwinian source for the bacterial flagellum, a tiny biological tail with a motor that is used as a model of design by the Intelligent Design movement. I would like to describe this T3SS to add to the previous information I have on Types II and IV.
(This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence 4.0 International.)
The drawing at top left (A) shows the bacteria using the T3SS to inject toxin into its victim. The system with number keys (B) is at right. The numbers label the protein components of the system. The lists at lower left (C) are two separate protein labeling systems for the T3SS. More details can be found at the article link given above.
As you can see, 20 different proteins are listed for this general depiction of the T3SS. Some are used multiple times.
More detailed looks at the needle complex are shown at the Research Collaboratory for Structural Bioinformatics Protein Data Bank (RCSB) entry 6Q15. These are based on an article from J Hu et al., "T3S injectisome needle complex structures in four distinct states reveal the basis of membrane coupling and assembly," Nature Microbiology 4, 11 (Nov. 2019): 2010-2019. The abstract is at the same web page given for the image (link at entry number). A side look:
The proteins interact with both the same and different proteins to form working structures. In the needle complex structure pictured above, the webpage lists 8 of the 20 proteins pictured in the Wagner image. Details of each are given, such as the number of amino acids per protein and depictions of the proteins isolated from each other. The first one listed, PrgK (number 4 on the Wagner image), has 252 amino acids. The second, PrgH (no. 5 on Wagner), has 392. The third, InvG (no. 1 on Wagner), has 562. The other counts of amino acids in this group of 8 range from 80 to 263.
And part of a base from another angle at RCSB 6PEM (same article citation as above is at this webpage, although this webpage lists only 6 proteins):
And part of a base from another angle at RCSB 6PEM (same article citation as above is at this webpage, although this webpage lists only 6 proteins):
At the website, these images can be manipulated in 3D. Hit the 3D View Structure link below the image.
Though I've had images before in this blog of the 20 biological amino acids, I'll show a chart here. They join together in a specific chemical formation to make the various proteins of our bodies.
These subunits must have the right shapes and charges in the right places for the T3SS to work. The system also requires energy from the respiration of the cell, an extremely complex system in its own right. It takes DNA and separate proteins to make these proteins and the bacterial cells must conduct other life-sustaining metabolism in the meantime.
Citation for RCSB: Helen M. Berman, John Westbrook, Zukang Feng, Gary Gilliland, T. N. Bhat, Helge Weissig, Ilya N. Shindyalov, Philip E. Bourne, "TheProtein Data Bank," Nucleic Acids Research 28, 1 (Jan. 1, 2000): 235–242.
As stated before, the T3SS is used as an example of a source for the bacterial flagellum, but it is described in authentic scientific literature as a complex system itself. Complex systems are found throughout all life and needed for survival. Together, they have almost countless atoms working in fabulous harmony. Where is their source?
Though Intelligent Design Theory technically defines the term "complexity" in relation to computer language, we do not have to be computer experts to understand the familiar meaning of the word "complex." People who believe God directly formed life can easily cite Romans 1:20, written by the Apostle Paul, "Ever since the creation of the world, his invisible attributes of eternal power and divinity have been able to be understood and perceived in what he has made…" (NABRE).
We all know about Galileo and the shifts of assumptions after discovery of planetary moons. But in the same way humanity was surprised because of what we learned in the scientific discipline of astronomy, we may well be even more surprised by biology. Many think a paradigm shift away from God came through reason, but the way back to God is even more logical if we cleanse ourselves of false premises. Let us not be afraid of dire "God of the Gaps" warnings. Of Jesus Christ, Paul said, “For in him were created all things in heaven and on earth…all things were created through him and for him” (Col. 1:16). Have faith that the more we discover, the more our knowledge will point us to appreciate all of God's handiwork.
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