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hmoment |
Periodicities in the polar/apolar character of the amino acid sequence of a protein can be examined by assigning to each residue a numerical hydrophobicity and searching for periodicity in the resulting one-dimensional function. The strength of each periodic component is the quantity that has been termed the hydrophobic moment.
When proteins of known three-dimensional structure are examined, it is found that sequences that form alpha helices tend to have, on average, a strong periodicity in the hydrophobicity of af 3.6 residues, the period of the alpha helix. The angle of rotation per residue in alpha helices is 100 degrees. Similarly, many sequences that form strands of beta sheets tend to have a periodicity in their hydrophobicity of about 2.3 residues, the period typical of beta structure. The angle of rotation per residue in beta sheets is 160 degrees. This means that many protein sequences tend to form the periodic structure that maximizes their amphiphilicity.
The hydrophobic moment is measured within a moving window using the method of Eisenberg et al. The default angle of 100 degrees is used for the alpha-helix results and the default of 160 degrees is used for the beta-sheet results. These angles can be changed if required using the appropriate options.
hmoment can plot two graphs when the option '-double' is given, one for the alpha helix moment and one for the beta sheet moment. Otherwise it just plots the alpha helix moment.
% hmoment sw:hbb_human Hydrophobic moment calculation Output file [hbb_human.hmoment]:
Mandatory qualifiers (* if not always prompted): [-seqall] seqall Sequence database USA * -graph xygraph Graph type * -outfile outfile Output file name Optional qualifiers: -window integer Window -bangle integer Beta sheet angle (degrees) Advanced qualifiers: -aangle integer Alpha helix angle (degrees) -baseline float Graph marker line -plot boolean Produce graphic -double boolean Plot two graphs General qualifiers: -help boolean Report command line options. More information on associated and general qualifiers can be found with -help -verbose |
Mandatory qualifiers | Allowed values | Default | |
---|---|---|---|
[-seqall] (Parameter 1) |
Sequence database USA | Readable sequence(s) | Required |
-graph | Graph type | EMBOSS has a list of known devices, including postscript, ps, hpgl, hp7470, hp7580, meta, colourps, cps, xwindows, x11, tektronics, tekt, tek4107t, tek, none, null, text, data, xterm, png | EMBOSS_GRAPHICS value, or x11 |
-outfile | Output file name | Output file | <sequence>.hmoment |
Optional qualifiers | Allowed values | Default | |
-window | Window | Any integer value | 10 |
-bangle | Beta sheet angle (degrees) | Any integer value | 160 |
Advanced qualifiers | Allowed values | Default | |
-aangle | Alpha helix angle (degrees) | Any integer value | 100 |
-baseline | Graph marker line | Any numeric value | 0.35 |
-plot | Produce graphic | Yes/No | No |
-double | Plot two graphs | Yes/No | No |
Otherwise it writes out a files containing the two columns separated by space or TAB characters. The first column is the position of the start of the window that the hydrophobic moment was calculated in. The second is the hydrophobic moment ('uH'). (If the option '-double' is given then the beta-sheet angle hydrophobicity is given as a third column.)
The ouput of the above is example follows:
HMOMENT of HBB_HUMAN from 1 to 146 Window: 10 Angle: 100 Max uH: 0.714 Position uH 1 0.091 2 0.216 3 0.208 4 0.123 5 0.211 6 0.194 7 0.185 8 0.169 9 0.312 10 0.292 11 0.185 12 0.092 13 0.050 14 0.164 15 0.245 16 0.187 17 0.130 18 0.262 19 0.396 20 0.317 21 0.342 22 0.492 23 0.508 24 0.517 25 0.418 26 0.416 27 0.350 28 0.292 29 0.196 30 0.102 31 0.288 32 0.314 33 0.442 34 0.560 35 0.464 36 0.577 37 0.584 38 0.676 39 0.714 40 0.670 41 0.462 42 0.369 43 0.221 44 0.176 45 0.073 46 0.058 47 0.041 48 0.148 49 0.125 50 0.219 51 0.221 52 0.110 53 0.060 54 0.045 55 0.107 56 0.264 57 0.259 58 0.401 59 0.452 60 0.354 61 0.265 62 0.365 63 0.430 64 0.522 65 0.508 66 0.519 67 0.349 68 0.324 69 0.330 70 0.365 71 0.447 72 0.364 73 0.251 74 0.166 75 0.118 76 0.252 77 0.276 78 0.299 79 0.330 80 0.241 81 0.315 82 0.291 83 0.163 84 0.182 85 0.254 86 0.069 87 0.179 88 0.201 89 0.065 90 0.041 91 0.110 92 0.181 93 0.261 94 0.312 95 0.200 96 0.263 97 0.369 98 0.310 99 0.362 100 0.495 101 0.585 102 0.450 103 0.488 104 0.547 105 0.315 106 0.311 107 0.252 108 0.187 109 0.215 110 0.295 111 0.425 112 0.303 113 0.421 114 0.528 115 0.487 116 0.436 117 0.501 118 0.532 119 0.409 120 0.447 121 0.308 122 0.383 123 0.252 124 0.361 125 0.374 126 0.314 127 0.219 128 0.310 129 0.361 130 0.439 131 0.433 132 0.507 133 0.336 134 0.344 135 0.207 136 0.234 137 0.299
Program name | Description |
---|---|
garnier | Predicts protein secondary structure |
helixturnhelix | Report nucleic acid binding motifs |
pepcoil | Predicts coiled coil regions |
pepnet | Displays proteins as a helical net |
pepwheel | Shows protein sequences as helices |
tmap | Displays membrane spanning regions |