Classical types

In the “classical” type system [1], a turn is partitioned into a type if three of the four dihedral angles of its two central residues lie within 30 degrees of the values given for the type in the table below, while the fourth lies within 40 degrees. In addition, membership in type VI (VIa1, VIa2, or VIb) requires a cis conformation for a turn's second peptide bond. The classical system also requires a proline residue at the third turn position for membership in type VI, but this requirement is dropped here, since the focus at the BB stage of turn mapping is entirely on BB geometry. If a turn does not meet the conditions for any structurally classified type, it is assigned to the structurally unclassified, "catch-all" type IV.

Ramachandran types

Scatterplot map of the (ϕ, ψ) BB dihedral angles of both central residues of all turns in the database, partitioned into the regions used to classify the turns into Ramachandran types [2, 3, 4]. In this system, a turn is classified by the regions occupied by the (ϕ, ψ) angles of its two central residues, along with the cis/trans status of its three peptide bonds. For example, if a turn's second and third residues fall in regions A and B respectively, while its first peptide bond is in cis conformation, the turn is assigned to Ramachandran type cisAB, while a turn with its central residues in regions B and P respectively and cis conformations for its second and third peptide bonds is type BcisPcis. Regions related by symmetry about the origin are labelled with the same letter, in uppercase for regions with negative ϕ values and lowercase for regions with positive ϕ values. Regions (A, D) and (a, d) represent right- and left-handed helical conformations respectively, while regions (B, b) represent beta conformations and regions (P, p) represent polyproline conformations. Points that fall outside the labelled regions are given the 'X' identifier.

A list of all 351 Ramachandran types present in the MapTurns/ExploreTurns database of 102,192 structures is given below the references, with types ordered by abundance in the database.

References

1) Hutchinson EG, Thornton JM. PROMOTIF--a program to identify and analyze structural motifs in proteins. Protein Science. 1996;5(2):212-220.

2) Shapovalov M, Vucetic S, Dunbrack RL. A new clustering and nomenclature for beta turns derived from high-resolution protein structures. PLOS Computational Biology. 2019;15(3).

3) Hollingsworth SA, Karplus PA. A fresh look at the Ramachandran plot and the occurrence of standard structures in proteins. Biomol Concepts. 2010;1(3-4):271-83.

4) Wilmot CM, Thornton JM. β-turns and their distortions: A proposed new nomenclature. Protein Eng. 1990;3(6):479-93.

Ramachandran types in the database

Type Count

-------------

AD 24321
AA 18651
Pd 10678
AB 8057
ad 3732
AZ 3441
Pa 3415
AN 2498
DD 2155
pD 1994
AG 1615
DZ 1473
Ba 1473

NA 1309

aa 1040

DA 1035

DN 996

DB 861

BcisP 836

pA 752

dN 685

AP 680

ND 622

PcisD 551

dD 536

Bd 483

NB 396

PA 326

Dd 321

Pg 312

pG 235

NZ 229

PcisP 216

dd 212

cisDA 208

NG 196

dZ 193

DG 187

gA 175

da 161

NN 155

Ga 153

gD 138

bD 133

PcisA 133

BcisD 122

bA 112

DP 109

aN 109

BcisA 108

NP 104

gB 104

Zd 100

Za 98

dA 97

Gd 95

cisAB 90

cisDP 87

pB 85

Bp 74

PX 74

PcisB 73

pZ 72

cisAA 70

ZcisP 66

Bg 62

pP 61

Ad 57

PD 55

XA 53

PcisG 50

cisDD 49

ag 47

PP 46

Gp 45

PG 45

BcisB 44

ABcis 43

XD 42

cisAP 39

cisDB 38

ap 36

Pp 35

DX 33

GD 31

gP 30

ab 30

cisDG 30

Xd 30

Gb 28

pa 25

aD 25

Zp 25

Da 25

dB 25

GN 24

acisP 21

cisAD 20

cisPd 20

PB 20

bG 20

GX 18

ZN 18

XZ 18

bP 16

cisPa 16

BcisG 16

gN 16

BX 15

gZ 15

ZcisB 15

XN 15

gG 15

AX 14

cisDZ 14

cisPP 14

PcisZ 14

Zg 13

Bb 13

db 13

pd 13

aX 13

bB 13

Dp 13

Gg 13

Bacis 13

ZcisD 12

cisBa 12

cisPcisP 12

BcisZ 12

GZ 12

cisGD 12

XB 11

ZD 11

DZcis 11

XX 11

XG 11

dp 11

cisAG 11

Xa 11

AZcis 10

Ab 10

ZcisA 10

PXcis 10

NBcis 9

bZ 9

Db 9

DAcis 9

ZX 9

XcisP 8

ZZ 8

cisDN 8

aZ 8

dP 8

pcisP 7

dG 7

cisAZ 7

Ap 7

AAcis 7

ZcisZ 7

AcisP 7

PZcis 6

Xg 6

DBcis 6

BcisPcis 6

Pb 6

GB 6

ZcisN 5

cisPcisD 5

ANcis 5

BA 5

NZcis 5

Dg 5

XcisB 5

pN 4

pcisg 4

Xp 4

cisPb 4

cisNA 4

cispB 4

pcisA 4

cisGA 4

cisPp 4

GcisB 4

cisBd 4

cisZD 4

NX 4

GA 4

PPcis 3

cisZA 3

BcisX 3

Zb 3

cisPcisA 3

GAcis 3

cisBX 3

ba 3

XP 3

cisABcis 3

Acisg 3

dX 3

cisPX 3

acisZ 3

aP 3

cisNZ 3

dg 2

Ncisg 2

cisXD 2

Bcisp 2

cisXB 2

cisAN 2

Abcis 2

aNcis 2

Gpcis 2

BcisN 2

pg 2

bcisP 2

PZ 2

Pbcis 2

DcisD 2

PBcis 2

APcis 2

aZcis 2

cisZd 2

ZNcis 2

cisGN 2

Zcisb 2

cisBN 2

acisD 2

AcisPcis 2

pX 2

cisGd 2

AcisX 2

ZA 2

cisND 2

BcisBcis 2

cisgB 2

BXcis 2

abcis 2

PcisAcis 2

ZG 2

PcisN 2

pcisD 2

cisGB 2

Dacis 2

bN 2

cisPPcis 2

Aa 2

Acisp 2

DXcis 1

aA 1

cisgN 1

Bcisg 1

pcisB 1

cisGZcis 1

cisGP 1

NNcis 1

gcisPcis 1

aPcis 1

NDcis 1

cisBcisN 1

Acispcis 1

pcisX 1

GP 1

XcisD 1

pcisG 1

cisZG 1

Bcisbcis 1

cisDpcis 1

AGcis 1

BBcis 1

cisDZcis 1

bcisPcis 1

cisgZ 1

dcisP 1

cisXA 1

Xb 1

XNcis 1

aB 1

AcisB 1

XcisZ 1

bcisp 1

cisAPcis 1

gBcis 1

cisgD 1

dAcis 1

cisdcisZ 1

NPcis 1

cisApcis 1

Acisdcis 1

gAcis 1

Gacis 1

cispP 1

Dpcis 1

dcisZ 1

cisXP 1

DcisZ 1

cisbZ 1

Zacis 1

GPcis 1

acisG 1

acisX 1

pZcis 1

cisPg 1

cisZg 1

cisGg 1

cisGX 1

cisGZ 1

NcisZ 1

cispG 1

cisNd 1

cisXG 1

AcisA 1

NcisX 1

cisAcisG 1

XcisA 1

cisDBcis 1

dNcis 1

cisNcisd 1

DcisA 1

cisDd 1

Bbcis 1

cispA 1

ZcisPcis 1

acisB 1

cisaX 1

Bpcis 1

Pcisp 1

NcisP 1

cispd 1

NcisAcis 1

cisAX 1

cisdX 1

Ncisp 1

cisaa 1

pcisp 1

cisNa 1

GG 1

PN 1

cisPA 1

cisBg 1

cisPcisB 1

DDcis 1

Acisa 1

bcisa 1

Pcisg 1

AXcis 1

PcisX 1

bcisB 1

cisBcisD 1

Nd 1

Apcis 1