The X-ray interpretation of denaturation and the structure of the seed globulins

Abstract

THE X-ray diffraction photographs usually obtained from apparently nonfibrous proteins have so much in common with one another and with the photographs given by certain natural protein fibres when disoriented that the inference seems clear that all proteins at some stage of their existence are fibrous in the molecular sense [Astbury, 1933; 1934,1,2]. Recently [Astbury and Lomax, 1934, 1, 2;1935] this concept has been expressed as a generalised interpretation of denaturation in the conclusion that the two more stable and insoluble states of protein structure, the fibrous and the denatured, are based on fundamentally similar modes of molecular arrangement; that, in fact, the denatured state2 is essentially a fibrous state inasmuch as it always consists of peptide chains, often fully extended, and aggregated after coagulation in parallel bundles, as in fibroin [Meyer and Mark, 1928], f3-keratin [Astbury and Street, 1931; Astbury and Woods, 1933], /3-myosin [Astbury and Dickinson, 1935], fibrin [Katz and De Rooy, 1933] etc. Itwas found that heat-denaturation of the albumins, for instance, merely makes the X-ray photograph more like that of a random arrangement of fibres of/-keratin (stretched hair, horn, etc.; cf. Plate V, Figs. 1 and 3). ,B-Keratin is built from almost fully-extended polypeptide chains linked side-to-side, firstly by combinations between their side-chains ("side-chain linkage "), and secondly in a direction at right angles [Astbury and Sisson, 1935], through attractions between the =CO and =NH groups of neighbouring main-chains ("backbone linkage"). The three-dimensional structure is that of a pile of polypeptide "grids ", the average distance apart of the main-chains in the plane of each grid being about 9*8 A. ("side-chain spacing") and the distance between the grids being 4*65 A. (" backbone spacing "). These two spacings correspond respectively to the two reflections, 001 and 200, seen on the equator of Fig. 4: they are the two prin'cipal side-spacings of the ,B-keratin crystallites, whilst the reflection 020 (spacing about 3*4 A.) gives the average length of an amino-acid residue in the direction of the main-chains. Fig. 4 is a "fibre photograph" of crystallites all pointing roughly in the same direction (the fibre-axis) and taken with the X-ray beam perpendicular to this direction; but when the crystallites are 1 Beit Scientific Research Fellow. 2 The seed globulins, at least, appear to pass through an intermediate fibrous state before reaching complete denaturation. It is possibly better therefore to reserve the word "denatured"

Studies on the Anomalous Viscosity and Flow-Birefringence of Protein Solutions

“…It has long been known that a molecule of ovalbumin, having a radius of 55.~ (Adair and Adair, 1940) unrolls into a surface fill of but 9.5A thickness (Astbury, Bell, Gorter, and van Ormondt, 1938). Some members of this group do it instantly (group B1) giving anomalous flow diagrams in the first instance, while others (group B~) require a considerable time to do so, and only give anomalous flow diagrams after the film has built itself up for half an hour or more.…”

“…Indeed, as long ago as 1882 yon Ebner, forcing out ovalbumin solutions into absolute alcohol through a capillary pipette, obtained highly birefringent fibrils. But the evidence which clinches the matter is that of Astbury, Bell, Gorter, and van Ormondt (1938) and Stenhagen (1938), who, building up piles of protein monolayers on a chromiumplated metal slide mechanically moving repeatedly through a protein film at an air-water interface (the technique of Blodgett, 1935;Blodgett and Langmuir, 1937), were able thus to produce multilayers containing from 1400 to 1800 layers of ovalbumin film, each one 9 to 10 A thick. Such multilayers, stripped from the metal base, were found to be birefringent (as much so as wool), while within them were often contained a multitude of negative tactoids, probably caused by the presence of minute foreign bodies, and showing at their edges an intense birefringence (as high as that of natural silk).…”

“…Lastly, if the above argument is sound, it is not without interest that in modern human technology, the preparation of actual fibres such as the artificial wool (lanital) from casein (yon Weimarn, 1927;Sutermeister and Browne, 1939, p. 215), plant seed globulins such as edestin and excelsin (Astbury, Dickinson, and Bailey, 1935;Labarre and Dostert, 1942), and soya bean protein (Sat6, 1923;Horvath, 1938) would be an instance of man having unknowingly made use of certain properties of proteins which have been, since the beginning of living things, essential to the life and development of cells and organisms.…”

“…Myosin.--Myosin was prepared from muscle tissue of rabbit and frog according to the standard methods (Edsall, 1930;Bailey, 1942). If the preparation is a good one, showing flow-birefringence, the viscosimeter behaviour is invariably the same, whether at low (film) level or flood (bulk) Details differ, thus in one experiment with myosin at low level (Experiment I 17/6b) the protein concentration was 0.0009 per cent in M KC1 and orientation was attained at some 70 R.P.M.…”

Truncated forms of the prion protein PrP demonstrate the need for complexity in prion structure

“…The ability of some proteins to fold into alternative, b-rich conformations has been known for over 80 y 1 Since that time, it has been determined that such b-rich conformations are the defining structural features of amyloid fibrils. The identification of prion rods as amyloid fibrils 2 is more recent, but still well-established.…”