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we know that Protein structures from secondary to Quaternary are maintained by noncovalent or weak interactions including electrostatic interactions,van der Waals forces & hydrogen bonding. What is the significance of these weak interactions why they are preferred by nature rather then strong covalent interactions?

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Proteins often undergo conformational changes. The activation energy required to undergo a conformational change in a protein with only covalent interactions would be much higher compared to that of a protein with weaker bonding forces. An example of a conformational change seen in enzymes is the change in conformation during allosteric regulation, in which an effector molecule binds a site on the enzyme distant from the enzymes active site. The binding of the effector molecule induces a conformational change that exposes the active site of the enzyme. Another example of conformational change is the change in conformation seen in Toll-Like-Receptors (TLRs). Additionally, many proteins change their conformation in response to pH. These changes would likely not occur if the protein only contained covalent bonds, and the ability of proteins to undergo such changes makes them responsive to the environment, as well as allowing them to carry out their enzymatic actions, if such actions exist for that particular protein.

Here is the wiki on allosteric regulation https://en.wikipedia.org/wiki/Allosteric_regulation

Here is a figure on conformational changes in TLRs http://www.nature.com/ni/journal/v8/n7/fig_tab/ni0707-675_F1.html

And here is the wiki on activation energy, a concept used in chemistry (see section on catalysis and Gibbs free energy) https://en.wikipedia.org/wiki/Activation_energy

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  • $\begingroup$ There are examples of covalent interactions that influence tertiary structure. One such example is a disulfide bridge. Check out this figure, where the two yellow balls constitute a disulfide bridge and influence tert structure i.ytimg.com/vi/ysPt1lIllcs/hqdefault.jpg $\endgroup$
    – DonJulian
    Dec 27, 2015 at 13:43
  • $\begingroup$ I know that one of the covalent interaction exist such as disulfide bridge my question was that majority of stabilizing forces are non covalent and what is significance behind this. $\endgroup$
    – katherinebridges
    Dec 27, 2015 at 14:29
  • $\begingroup$ Please see my answer above. I believe it is what you are looking for. The non-covalent interactions allow the protein to easily change conformation. This makes the protein dynamic and responsive. $\endgroup$
    – DonJulian
    Dec 27, 2015 at 14:33
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    $\begingroup$ Conversely, if the protein only contained covalent bonds, its structure would be rigid, and it would require much higher activation energies to change conformation (compare the changes in enthlapy between breaking a covalent bond and breaking a hydrogen bond). $\endgroup$
    – DonJulian
    Dec 27, 2015 at 14:35
  • $\begingroup$ yes, I find it useful.. $\endgroup$
    – katherinebridges
    Dec 27, 2015 at 20:45

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