text: user2817: I came across an article which has defined 3 categories: Buried [A, L, F, C, G, I, V, W], Exposed [ R, K, Q, E, N, D] and Intermediate [M, S, P, T, H, Y] when analyzing the solvent accessibility of a protein. But I could not find any reference validating the claim. 
  Another article has come up with 4 divisions:
  B=completely buried (0-4% exposed)
  b=partly buried (4-25% exposed)
  e=partly exposed (25-50% exposed)
  E=completely exposed (50+% exposed)   
  Which is authentic when dealing with solvent accessibility, and which should be used? Also for the second article [B,b,e,E], which amino acid corresponds to which class?
  
  user266: There is some confusion in the question.
  Solvent accessibility of a residue, i.e. the area accessible to the solvent (water), depends on the 3D structure of the protein. It's not a property of  an amino-acid (chemical compound such as alanine, leucine, ...).
  There may be a correlation -- amino-acids with hydrophobic side chains are more likely to be buried, but in general amino-acids (chemical compounds) cannot be classified as buried or exposed.
  I don't have access to the first article, but I tried running the prediction server described in the second linked article, and I got a result
  GSGMQIFVKTFRDRLRNLLPQTITLEVEPSDTIENVKAKIQDKEGIPPDQQVLIFSRKRL
  CCCCEEEEEECEEEEEECCCCEEEEEECCCCCHHHHHHHHHHHHCCCHHHEEEEECCEEC
  EEEBeBbBebbEbEbEebEEeEbeBEBeeEeeBeeBbEeBeEeEEbEeEeBeBbbEEeeb
  
  ...
  
  Porter (Secondary Structure):
  H = Helix   (DSSP classes H, G and I)
  E = Strand  (DSSP classes E and B)
  C = Coil    (DSSP classes S, T and .)
  
  PaleAle (Relative Solvent Accessibility):
  B = very buried      (<=4% accessible)
  b = somewhat buried  (>4% and <=25% accessible)
  e = somewhat exposed (>25% and <=50% accessible)
  E = very exposed     (>50% accessible)
  
  In one place in the sequence you can see QQ, predicted as eB.
  So clearly glutamine is NOT assigned to a particular RSA class.
  Dividing RSA (relative solvent accessibility, 0-100%) into categories is arbitrary, I don't think there is any widely used convention. The easiest way would be to just use numeric values.
  
original_text: 2817: <p>I came across an <a href="https://academic.oup.com/bioinformatics/advance-article-abstract/doi/10.1093/bioinformatics/bty155/4934942?redirectedFrom=fulltext" rel="nofollow noreferrer">article</a> which has defined 3 categories: Buried [A, L, F, C, G, I, V, W], Exposed [ R, K, Q, E, N, D] and Intermediate [M, S, P, T, H, Y] when analyzing the solvent accessibility of a protein. But I could not find any reference validating the claim. </p>
  
  <p>Another <a href="https://academic.oup.com/bioinformatics/article/29/16/2056/204670" rel="nofollow noreferrer">article</a> has come up with 4 divisions:</p>
  
  <p>B=completely buried (0-4% exposed)<br>
  b=partly buried (4-25% exposed)<br>
  e=partly exposed (25-50% exposed)<br>
  E=completely exposed (50+% exposed)   </p>
  
  <p>Which is authentic when dealing with solvent accessibility, and which should be used? Also for the second article [B,b,e,E], which amino acid corresponds to which class?</p>
   266: <p>There is some confusion in the question.</p>
  
  <p>Solvent accessibility of a residue, i.e. the area accessible to the solvent (water), depends on the 3D structure of the protein. It's not a property of  an amino-acid (chemical compound such as alanine, leucine, ...).</p>
  
  <p>There may be a correlation -- amino-acids with hydrophobic side chains are more likely to be buried, but in general amino-acids (chemical compounds) cannot be classified as buried or exposed.</p>
  
  <p>I don't have access to the first article, but I tried running the prediction server described in the second linked article, and I got a result</p>
  
  <pre><code>GSGMQIFVKTFRDRLRNLLPQTITLEVEPSDTIENVKAKIQDKEGIPPDQQVLIFSRKRL
  CCCCEEEEEECEEEEEECCCCEEEEEECCCCCHHHHHHHHHHHHCCCHHHEEEEECCEEC
  EEEBeBbBebbEbEbEebEEeEbeBEBeeEeeBeeBbEeBeEeEEbEeEeBeBbbEEeeb
  
  ...
  
  Porter (Secondary Structure):
  H = Helix   (DSSP classes H, G and I)
  E = Strand  (DSSP classes E and B)
  C = Coil    (DSSP classes S, T and .)
  
  PaleAle (Relative Solvent Accessibility):
  B = very buried      (&lt;=4% accessible)
  b = somewhat buried  (&gt;4% and &lt;=25% accessible)
  e = somewhat exposed (&gt;25% and &lt;=50% accessible)
  E = very exposed     (&gt;50% accessible)
  </code></pre>
  
  <p>In one place in the sequence you can see <code>QQ</code>, predicted as <code>eB</code>.
  So clearly glutamine is NOT assigned to a particular RSA class.</p>
  
  <p>Dividing RSA (relative solvent accessibility, 0-100%) into categories is arbitrary, I don't think there is any widely used convention. The easiest way would be to just use numeric values.</p>
  