@text 
"THE DISULFIDE BRIDGE -- STRUCTURAL STABILIZATION OF PROTEINS"

Ribonuclease A, a small single-subunit enzyme that cuts RNA, is an excellent example of a protein held together by disulfide bridges (from PDB file, 5RSA).  Each of the bridges is the result of two cysteine sidechains in close proximity (as a result of protein folding) undergoing covalent attachment through the terminal sulfurs; the chemical reaction can be depicted as follows:  -S-H + H-S-  =>  -S-S-.  This reaction occurs under oxidative conditions, typically found in extracellular regions.  One or more disulfide bridges can be found to connect domains within a protein (intramolecular bridges).  They can also be found in multi-subunit proteins between individual polypeptide chains (intermolecular bridges).  The disulfide bridge is critical for maintaining the active conformation in many proteins.  In fact, breaking disulfide bonds through reductive processes yields a protein with significantly lower activity.
@kinemage 1 
@caption 
Calpha trace of RNase A, with the four disulfide bridges highlighted.  Cysteine sulfurs are depicted as gold balls; carbons are green balls.  Select view2 for a close-up of one disulfide bond, showing the connection between two sequentially-removed portions of the protein.
@onewidth
@viewid {4 S-S}
@zoom 1.00 
@zslab 170 
@center 30.267 16.026 13.157 
@matrix 
-0.812147 0.424353 0.400427 0.385290 0.905445 -0.178101 -0.438142 0.009636 -0.898854
@2viewid {Close-up}
@2zoom 2.28 
@2zslab 200 
@2center 20.048 4.269 7.736 
@2matrix 
 0.04866  0.22040  0.97419 -0.05760  0.97435 -0.21756 -0.99715 -0.04553  0.06011
@group {RNase} 
@subgroup {Calphas} dominant
@vectorlist {ca-ca} color=bluetint
{ca lys 1}P 17.372 25.599 -1.318
{ca lys 1}17.372 25.599 -1.318
{ca glu 2}19.195 24.738 1.949
{ca thr 3}22.383 26.747 2.254
{ca ala 4}25.655 25.012 3.159
{ca ala 5}25.736 27.038 6.419
{ca ala 6}22.196 25.871 7.429
{ca lys 7}23.094 22.309 6.327
{ca phe 8}26.126 22.443 8.706
{ca glu 9}23.823 23.393 11.561
{ca arg 10}21.305 20.65 10.749
{ca gln 11}23.953 17.905 10.428
{ca his 12}26.354 18.986 13.14
{ca met 13}24.937 21.262 15.889
{ca asp 14}23.324 20.085 19.089
{ca ser 15}23.317 23.068 21.463
{ca ser 16}20.431 21.717 23.489
{ca thr 17}22.3 18.924 25.178
{ca ser 18}25.724 19.105 26.864
{ca ala 19}26.624 15.565 25.829
{ca ala 20}24.865 12.381 24.626
{ca ser 21}23.329 10.656 27.632
{ca ser 22}22.353 7.236 26.351
{ca ser 23}23.626 4.814 23.731
{ca asn 24}20.527 5.723 21.601
{ca tyr 25}21.579 9.308 21.
{ca cys 26}23.014 8.67 17.523
{ca asn 27}20.094 6.558 16.399
{ca gln 28}17.684 9.242 17.476
{ca met 29}19.612 12.297 16.155
{ca met 30}20.678 10.819 12.817
{ca lys 31}17.079 10.067 12.038
{ca ser 32}15.551 13.273 13.405
{ca arg 33}18.032 15.515 11.515
{ca asn 34}17.073 13.558 8.4
{ca leu 35}20.597 12.158 7.798
{ca thr 36}19.289 8.698 7.014
{ca lys 37}16.628 9.595 4.496
{ca asp 38}18.199 8.483 1.26
{ca arg 39}20.803 6.147 2.77
{ca cys 40}22.661 5.563 6.06
{ca lys 41}25.326 8.318 6.297
{ca pro 42}28.209 6.182 7.715
{ca val 43}29.703 8.693 10.044
{ca asn 44}28.6 11.954 11.588
{ca thr 45}29.66 14.248 14.475
{ca phe 46}27.37 16.426 16.627
{ca val 47}28.781 19.448 18.564
{ca his 48}27.264 20.375 21.971
{ca glu 49}28.155 24.015 22.153
{ca ser 50}26.545 27.276 21.16
{ca leu 51}26.477 27.996 17.474
{ca ala 52}28.243 31.265 18.166
{ca asp 53}31.217 29.382 19.714
{ca val 54}31.306 27.078 16.71
{ca gln 55}31.102 29.939 14.152
{ca ala 56}33.979 31.61 16.001
{ca val 57}36.263 28.738 15.015
{ca cys 58}36.355 30.441 11.593
{ca ser 59}38.661 32.967 13.126
{ca gln 60}40.865 30.508 15.078
{ca lys 61}43.771 28.489 13.841
{ca asn 62}44.119 28.064 10.104
{ca val 63}44.984 24.473 9.04
{ca ala 64}44.908 22.532 5.726
{ca cys 65}41.706 20.374 5.582
{ca lys 66}42.295 16.648 5.244
{ca asn 67}41.767 16.991 1.441
{ca gly 68}44.475 19.8 1.126
{ca gln 69}42.078 22.81 1.058
{ca thr 70}43.304 25.794 2.987
{ca asn 71}40.023 27.051 4.332
{ca cys 72}39.994 24.79 7.457
{ca tyr 73}40.274 26.059 11.007
{ca gln 74}41.025 24.28 14.3
{ca ser 75}39.372 25.191 17.524
{ca tyr 76}41.739 26.688 20.084
{ca ser 77}39.634 24.841 22.715
{ca thr 78}38.27 21.283 23.228
{ca met 79}34.531 20.902 22.689
{ca ser 80}31.922 18.307 23.794
{ca ile 81}31.23 16.162 20.682
{ca thr 82}29.306 12.947 19.978
{ca asp 83}30.66 10.719 17.189
{ca cys 84}28.149 8.458 15.469
{ca arg 85}29.399 5.472 13.529
{ca glu 86}27.35 2.965 11.598
{ca thr 87}27.128 -0.521 13.258
{ca gly 88}27.443 -3.946 11.608
{ca ser 89}23.734 -4.283 12.167
{ca ser 90}22.876 -1.102 10.179
{ca lys 91}20.42 -1.864 7.36
{ca tyr 92}18.716 0.868 5.308
{ca pro 93}16.13 2.157 6.251
{ca asn 94}17.022 0.873 9.776
{ca cys 95}20.312 2.786 10.06
{ca ala 96}21.986 1.836 13.354
{ca tyr 97}24.785 3.76 15.03
{ca lys 98}27.283 3.427 17.84
{ca thr 99}27.401 6.646 19.974
{ca thr 100}30.772 7.905 21.248
{ca gln 101}30.94 11.023 23.62
{ca ala 102}34.288 12.903 23.746
{ca asn 103}35.891 16.305 24.348
{ca lys 104}38.228 17.262 21.499
{ca his 105}39.259 20.038 19.28
{ca ile 106}37.228 20.423 16.112
{ca ile 107}38.339 21.218 12.514
{ca val 108}35.828 22.861 10.164
{ca ala 109}35.962 24.395 6.635
{ca cys 110}34.607 28.006 6.449
{ca glu 111}33.224 29.981 3.507
{ca gly 112}31.175 33.073 2.538
{ca asn 113}30.36 36.335 4.24
{ca pro 114}29.722 36.156 7.076
{ca tyr 115}32.526 33.511 7.056
{ca val 116}30.914 30.521 8.817
{ca pro 117}31.375 26.739 9.073
{ca val 118}30.091 24.766 6.025
{ca his 119}31.851 21.421 6.622
{ca phe 120}32.927 19.335 9.591
{ca asp 121}36.407 18.112 8.76
{ca ala 122}37.727 16.178 11.842
{ca ser 123}37.937 16.116 15.637
{ca val 124}41.435 16.025 17.085
@subgroup {S-S} dominant
@vectorlist {ss} color=yellow
{ca cys 65}P 41.706 20.374 5.582
{cb cys 65}40.613 20.618 4.569
{sg cys 65}39.9 22.235 4.768
{sg cys 72}39.222 22.229 6.587
{cb cys 72}40.379 23.319 7.468
{ca cys 72}39.994 24.79 7.457
{ca cys 26}P 23.014 8.67 17.523
{cb cys 26}24.314 7.997 17.133
{sg cys 26}25.715 8.896 17.715
{sg cys 84}26.015 10.222 16.198
{cb cys 84}26.935 9.216 14.986
{ca cys 84}28.149 8.458 15.469
{ca cys 40}P 22.661 5.563 6.06
{cb cys 40}22.867 4.192 6.728
{sg cys 40}21.405 3.143 6.86
{sg cys 95}20.048 4.269 7.736
{cb cys 95}20.502 4.196 9.498
{ca cys 95}20.312 2.786 10.06
{ca cys 58}P 36.355 30.441 11.593
{cb cys 58}35.255 30.831 10.619
{sg cys 58}34.266 29.409 10.161
{sg cys 110}35.415 28.241 9.096
{cb cys 110}35.099 29.042 7.474
{ca cys 110}34.607 28.006 6.449
@balllist {C} radius=.3 color=green
{ca cys   65 } P 41.706, 20.374, 5.582
{cb cys   65 } L 40.613, 20.618, 4.569
{cb cys   72 } L 40.379, 23.319, 7.468
{ca cys   72 } L 39.994, 24.790, 7.457
{ca cys   26 } P 23.014, 8.670, 17.523
{cb cys   26 } L 24.314, 7.997, 17.133
{cb cys   84 } L 26.935, 9.216, 14.986
{ca cys   84 } L 28.149, 8.458, 15.469
{ca cys   40 } P 22.661, 5.563, 6.060
{cb cys   40 } L 22.867, 4.192, 6.728
{cb cys   95 } L 20.502, 4.196, 9.498
{ca cys   95 } L 20.312, 2.786, 10.060
{ca cys   58 } P 36.355, 30.441, 11.593
{cb cys   58 } L 35.255, 30.831, 10.619
{cb cys   110 } L 35.099, 29.042, 7.474
{ca cys   110 } L 34.607, 28.006, 6.449
@balllist {S} radius=.3 color=gold
{ sg  cys   65 } L 39.900, 22.235, 4.768
{ sg  cys   72 } L 39.222, 22.229, 6.587
{ sg  cys   26 } L 25.715, 8.896, 17.715
{ sg  cys   84 } L 26.015, 10.222, 16.198
{ sg  cys   40 } L 21.405, 3.143, 6.860
{ sg  cys   95 } L 20.048, 4.269, 7.736
{ sg  cys   58 } L 34.266, 29.409, 10.161
{ sg  cys   110 } L 35.415, 28.241, 9.096
<end of file>