Several computational methods exist for the identification of transmembrane beta 
barrel proteins (TMBs) from sequence. Some of these methods also provide the 
transmembrane (TM) boundaries of the putative TMBs. The aim of this study is to 
(1) derive the propensities of the TM residues to be exposed to the lipid 
bilayer and (2) to predict the exposure status (i.e. exposed to the bilayer or 
hidden in protein structure) of TMB residues. Three novel propensity scales 
namely, BTMC, BTMI and HTMI were derived for the TMB residues at the hydrophobic 
core region of the outer membrane (OM), the lipid-water interface regions of the 
OM, and for the helical membrane proteins (HMPs) residues at the lipid-water 
interface regions of the inner membrane (IM), respectively. Separate propensity 
scales were derived for monomeric and functionally oligomeric TMBs. The derived 
propensities reflect differing physico-chemical properties of the respective 
membrane bilayer regions and were employed in a computational method for the 
prediction of the exposure status of TMB residues. Based on the these 
propensities, the conservation indices and the frequency profile of the 
residues, the transmembrane residues were classified into buried/exposed with an 
accuracy of 77.91% and 80.42% for the residues at the membrane core and the 
interface regions, respectively. The correlation of the derived scales with 
different physico-chemical properties obtained from the AAIndex database are 
also discussed. Knowledge about the residue propensities and burial status will 
be useful in annotating putative TMBs with unknown structure.