Biological complexity: contingency planning (Introduction)

by David Turell , Wednesday, May 05, 2021, 22:02 (1298 days ago) @ David Turell

How does 'what if' contingency planning appear in cell function?:

https://evolutionnews.org/2021/05/contingency-planning-in-the-cell-affirms-design/

Collagen is the most abundant protein in the human body. When collagen fibers are assembled, there’s a polysaccharide that usually sits idly by. It is called N-glycan, and its role has remained elusive for decades. Now, scientists have figured out what it’s there for. Rasia C. Li et al., publishing in PNAS, announced that “Collagen’s enigmatic, highly conserved N-glycan has an essential proteostatic function.” The team figured that this member must have a function because it is highly conserved in all domains of life despite the energetic cost of maintaining it. With that knowledge, they searched for its elusive purpose.

By assaying N-glycan function under conditions of impaired collagen folding, we show that, although the N-glycan is dispensable under normal conditions, it is essential for collagen folding and secretion under conditions that challenge proteostasis. Such environments are commonly encountered during development, tissue repair, and disease.

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A 2017 textbook on the Essentials of Glycosylation spends several pages describing the synthesis of N-glycans. It takes a lot of cellular machinery to construct these players! “The biosynthesis of N-glycans is most complex in mammals,” the three authors say. There are processes to make the nascent molecule, then there are early processing steps, late processing steps and maturation steps. These occur in two cellular compartments: the Golgi and the endoplasmic reticulum.

N-Glycan synthesis begins on a lipid-like polyisoprenoid molecule termed dolichol-phosphate (Dol-P) in eukaryotes. Following synthesis of an oligosaccharide that contains as many as 14 sugars, the N-glycan is transferred “en bloc” to protein. This synthetic pathway is conserved in all metazoa, plants, and yeast…. N-Glycans affect many properties of glycoproteins including their conformation, solubility, antigenicity, activity, and recognition by glycan-binding proteins…. Defects in N-glycan synthesis lead to a variety of human diseases.

Comment: Protective mechanisms of this must be present when the initial system is designed. It cannot be developed from observing mistakes as there would have been a stop to their evolution. Only design fits.