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Types of stretching and the effects on flexibility
Published in David G. Behm, The Science and Physiology of Flexibility and Stretching, 2018
Collagen consists of long, fibrous structural proteins with high tensile strength and is the main component of fascia, cartilage, ligaments, tendons, bone. and skin (123) (Figure 3.8). It is an evolutionary ancient protein involved with the binding of cells of the simplest animals, such as sponges, as well as humans (124). Collagen has an extremely low compliance, similar to the tensile characteristics of copper. Intermolecular cross-links stabilize collagen, preventing the long rod-like molecules from sliding past each other, forming almost inextensible fibres (125). In combination with the proteins – elastin and soft keratin – their mix provides not only strength (collagen) but also elasticity (elastin) (126). Unlike collagen, elastin can double its length (125). With ageing, collagen increases markedly (126), which would have significant effects on ROM. The low compliance of collagen increases muscle, tendon, and ligament stiffness. Thus, with increased stiffness or lower compliance, higher passive tension occurs for smaller increases in musculotendinous length. These changes would also have significant effects on the stretch-shortening cycle. An increase in connective tissue proteins such as collagen impede the muscle contraction/relaxation process because it would have less extensible and compressible spring-like capabilities (126). A further complication is the excessive formation of intermolecular cross-links (124). Collagen and elastin cross-links in younger people promote strength and elasticity in the tissue, but excessive cross-links with ageing can ensure that stiffness predominates over compliance. Another age-related change is the decreased hydration (water content) of aged tissue. Proteoglycans (i.e. chondroitin sulphate and keratin), which are present in virtually all extracellular matrices of connective tissues, can hold large amounts of water, and so changes in their composition could lead to mild dehydration and some loss of function and extensibility (124). An example of this lack of extensibility with age can be seen with a simple test. Have a young person (especially a child) and a senior adult pinch the skin on the back of the hand. Then, quickly release the skin and be aware of the time it takes for the skin to return to its original shape and position. In a young child, it is practically instantaneous and would be almost impossible to measure with a stop watch or timer. With a senior adult, you can easily see and measure the slow return of the pinched skin to its original position. The older person’s more dehydrated, cross-linked, collagen-predominant skin lacks the elasticity of the young person’s skin. The same processes occur in the older person’s connective tissues subcutaneously (under the skin) with the muscles, tendons, ligaments, and other tissues.
Proteomes of the past: the pursuit of proteins in paleontology
Published in Expert Review of Proteomics, 2019
The gold-standard for protein detection is sequencing by mass spectrometry. A half dozen papers report short sequences from Cretaceous samples, though they remain contentious. Asara and coworkers published the tryptic peptide collagen sequence GVQPP(OH)GPQGPR and five others from T. rex femur bone extract [96]. Ancient protein experts Buckley and Collins led a study to refute that claim. Their rebuttal paper showed experimental decay data to substantiate the argument that collagen cannot last that long [9]. In response, Asara and Schweitzer relisted all six T. rex collagen peptides and noted the multiple separate contaminations required to produce their data as unlikely [97]. Mass spectrometrist Bern and colleagues reanalyzed the T. rex mass spectra and found no problems with the initial results [12]. Their re-analysis also revealed fragments of hemoglobin sequence. More recently, Saitta and coworkers did not find collagen, but did find microbes in a Cretaceous Centrosaurus bone [98]. They concluded that published reports mistook bacterial contamination for Cretaceous collagen despite the possibility of collagenous signals in bones other than their selected sample.
Protein evolution revisited
Published in Systems Biology in Reproductive Medicine, 2018
Peter L. Davies, Laurie A. Graham
These four AFP types are so different that they have obviously evolved independently to counter the possibility of teleosts freezing in seawater. Binding to ice has not been a persistent necessity, unlike electron transfer served by cytochrome c, where phylogenetic relationships can be mapped from the amino acid changes in the same protein going back to the common single-celled ancestors of all the major kingdoms, and recapitulate the phylogenetic tree deduced by anatomical relationships. Another example of an ancient protein family that featured prominently in ‘Mechanisms of Protein Evolution’ (Dixon 1966) are the oxygen carriers myoglobin and hemoglobin, which were needed after photosynthesis polluted the atmosphere with oxygen ~2.3 billion years ago and multicellular organisms evolved to use oxygen as a terminal electron acceptor (Lyons et al. 2014; Luo et al. 2016). No, antifreeze in fish is a recent need we have traced back to global cooling which took place during the latter half of the Eocene (Scott et al. 1986). Ice first appeared around 47 million years ago (mya) (Stickley et al. 2009; Tripati and Darby 2018), but teleosts arose between 200 and 300 mya, during part of which time the Earth was in a greenhouse climate state (Pross et al. 2012). Cooling accelerated when continental drift opened the Drake Passage around 40 mya and Antarctica became isolated at the South Pole by the circumpolar current (Scher and Martin 2006). Sea-level glaciation would have introduced no-go zones for unprotected teleosts. However, those fortunate fish species that developed AFPs would have had access to a niche devoid of other teleosts. Here, they could feed on invertebrates (which are isotonic with sea water and do not need AFPs), with less competition or risk of predation. The rapid speciation of a pioneering AFGP-producing nototheniod, whose descendants occupy almost every niche of the Antarctic Ocean, is a good illustration of the selective advantage of having the means to inhibit ice growth within the body (Near et al. 2012). There are parallels here to the adaptive radiation of Darwin’s finches that now occupy many niches, having been the first land bird to colonize the recently emerged Galapagos Islands (Almén et al. 2016).