PRESENTED BY:SABARNI SARKER

HISTORY OF PROTEIN DISCOVERY

• The similarity between the cooking of egg whites and the curdling of milk was recognized even in ancient times; for example, the name albumen for the egg-white protein was coined by Pliny the Elder (a scholar from ancient Rome) from the Latin albus ovi (egg white).

Pre-history of Protein

Ancient people new much about the similarity of egg white and curdled milk

• There had been the concept of an "animal substance," slight variants of which were thought to make up muscles, skin, and blood.

• But it turned into hard, hornlike material when heated and became foul-smelling when kept under moist, warm conditions, giving off an alkaline vapor.

• This contrasted with the properties of starch and sugar.

• In 1728, the Italian scholar Jacopo Beccari announced that he had discovered the presence of a material with all the characteristics of "animal substance" in white wheat flour.

Pre-history of Protein

• Proteins were recognized as a distinct class of biological molecules by Antoine Fourcroy at 1789

• Members of this class were called albuminoids• Well-known examples at the start of the

nineteenth century included albumen from egg whites, blood serum albumin, fibrin, and wheat gluten

Protein: A Distinct Class

• Dutch chemist Gerhardus Johannes Mulder carried out elemental analyses of common animal and plant proteins in 1837

• To everyone's surprise, all proteins had nearly the same empirical formula, roughly C400H620N100O120 with individual sulfur and phosphorus atoms.

• He hypothesized that there was one basic substance (Grundstoff) of proteins, and that it was synthesized by plants and absorbed from them by animals in digestion.

PROTEIN: THE GRUNDSTOFF

Nomenclature of the protein

• Berzelius supported the theory of Mudler.• He proposed the name "protein" for this

substance in a letter dated 10 July 1838.• He said: The name protein that I propose for

the organic oxide of fibrin and albumin, I wanted to derive from the Greek word πρωτειος (first; foremost), because it appears to be the primitive or principal substance of animal nutrition.

Gerardus Johannes Mulder(1802-1880)

Jöns Jacob Berzelius(1779-1848)

Protein Timeline• 1819: Leucine is the first amino acid isolated. The 20th,

threonine, was not discovered until 1936. • 1902: Emil Fisher and Franz Hofmeister (independently)

discover the peptide bond.• 1907-8: Committees in England and the USA standardise

the term protein.• 1920: Hermann Staudinger was the first effective

proponent of the idea that true molecules of huge size are capable of stable existence.

• 1925: N. Bjerrum, E. Q. Adams, K. Linderstrøm-Lang and others reach consensus about the zwitterionic character of proteins at the isoelectric pH.

Protein Timeline (Continued)• 1929, Hsien Wu hypothesized that denaturation was

protein unfolding, a purely conformational change that resulted in the exposure of amino acid side chains to the solvent.

• 1930-1950, The hypothesis of protein folding was followed by research into the physical interactions that stabilize folded protein structures.

• The secondary and low-resolution tertiary structure of globular proteins was investigated initially by hydrodynamic methods. After 1950, Spectroscopic methods to probe protein structure were developed.

And Finally!• The first atomic-resolution structures of proteins

were solved by X-ray crystallography in the 1960s and by NMR in the 1980s.

• As of 2006, the Protein Data Bank has nearly 40,000 atomic-resolution structures of proteins.

• In more recent times, cryo-electron microscopy of large macromolecular assemblies and computational protein structure prediction of small protein domains are two methods approaching atomic resolution.

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