Neil Voss <vossman77@yahoo.com>, 2003-2009
Craig Yoshioka <craigyk@gmail.com>, 2009

REFERENCE
  Voss NR, Gerstein M, Steitz TA, Moore PB.
  "The geometry of the ribosomal polypeptide exit tunnel."
  J Mol Biol. 2006 Jul 21;360(4):893-906.
   PMID: 16784753
   DOI: http://dx.doi.org/10.1016/j.jmb.2006.05.023

The geometry of the polypeptide exit tunnel has been determined using the crystal structure 
of the large ribosomal subunit from Haloarcula marismortui. The tunnel is a component of a 
much larger, interconnected system of channels accessible to solvent that permeates the 
subunit and is connected to the exterior at many points. Since water and other small 
molecules can diffuse into and out of the tunnel along many different trajectories, the 
large subunit cannot be part of the seal that keeps ions from passing through the 
ribosome-translocon complex. The structure referred to as the tunnel is the only passage in 
the solvent channel system that is both large enough to accommodate nascent peptides, and 
that traverses the particle. For objects of that size, it is effectively an unbranched tube 
connecting the peptidyl transferase center of the large subunit and the site where nascent 
peptides emerge. At no point is the tunnel big enough to accommodate folded polypeptides 
larger than alpha-helices.
