Richard Dickerson estimated in 1978 that the structures of about 132 soluble proteins had been determined to sufficient resolution for the backbone to be traced (see PDB Newsletter Number 13, Spring 2002, p. 3). From a plot of the number of new structures per year (n) versus years (y), he determined that n = exp(ay) with a = 0.19. This growth rate predicted about 13,000 structures by 2001 — which turned out to be remarkably accurate. Dickerson's letter was written 18 years after the publication (Kendrew et al., 1960) of the first high-resolution protein structure in 1960. The same amount of time has now elapsed since the publication (Deisenhofer et al., 1985) of the first high-resolution structure of a membrane protein in 1985. What has our progress been in this challenging field relative to soluble proteins, and what might the future hold?
Using data from the database of membrane proteins of known 3D structure that my laboratory maintains, there were 75 unique membrane protein structures at the close of 2003. An analysis similar to Dickerson's yields a = 0.14 (data not shown). The eighteen-year cumulative exponential growths of new structures for both soluble and membrane proteins are shown above. The growth rate suggests that we can expect the number of new MP structures to exceed 100 some time in 2005. And by 2025? About 2200.
Notes: This material is derived from an article published by S. H. White in Protein Science. In the above figure, the data for soluble proteins (red squares) are from a letter written in 1978 by Richard Dickerson (http://www.rcsb.org/pdb/dickerson.letter.html). The data for membrane proteins (MPs; solid blue circles) were compiled from data available at this web site. 'New' MP structures includes the same protein from different organisms, but excludes structures of mutagenized versions of proteins already in the database. Structures that differ only by the substrate bound or by physiological state are also excluded. The solid curves are fits of the data to the equation m = exp(by), where m is the cumulative total of new structures and y is the number of years since the publication of the first structure. The parameter b = 0.289 and 0.242 for soluble and MPs, respectively. The data for MPs suggest that there will be more than 100 structures some time in 2005.
Deisenhofer J., Epp O., Miki K., Huber R., and Michel H. 1985. Structure of the protein subunits in the photosynthetic reaction centre of Rhodospeudomonas viridis at 3 Å resolution. Nature 318:618-624.
Kendrew J.C., Dickerson R.E., Strandberg B.E., Hart R.G., and Davies D.R. 1960. Structure of myoglobin: A three-dimensional Fourier synthesis at 2 Å resolution. Nature 185:422-427.