BOS  CHICK Yeast  Y.Pre  Rb.s Rb.c
H S56   T56   E46   E76   W32   W32   
H Q57   Q57   T47   T77   P33   P33   
H F58   F58   F48   F78   L34   L34 cut(?) by Cht (N. crassa)	
H V59   I59   I49   I79   I35   I35   
H S60   S60   S50   S80   N36   N36   
H S61   S61   S51   S81   Q37   Q37   
  M62   L62   M52   M82   M38   M38   
  S63   S63   T53   T83   N39   N39   
  A64-| A64   A54   A84   P40   A40   
  S65 | S65   T55   T85   S41   S41   
G A66-| A66   A56   A86   A42   A42__Cut by cht in Pc (10%)(SdeV)
G D67 | D67   D57   D87   D43   D43  cut by endog.(Rb), TL(bov)
G V68-| V68   V58   V88   V44   V44 P  
  L69 | L69   L59   L89   Q45   K45 P_ Cut by cht in Pc (80%)
  A70-| A70   A60   A90   A46   A46 P +2ALA, cut by TL (Rb)	
  M71   L71   M61   M91   L47   M47 P_ Cut by cht in Pc (10%) 
  S72   S72   A62   A92   A48   A48 P  
  K73   K73   K63   K93   S49   S49 P  
  I74   I74   V64   V94   I50   I50   
  E75   E75   E65   E95   F51   F51   
 BOS  CHICK Yeast  Y.Pre  Rb.s Rb.c

The ISP erupts from the surface of cytochrome b at the level of residue 66,  which has a strong backbone N H-bond with cyt b residue 72 (O) in the same monomer. The next residue, 67, has an H-bond/ionpair between its conserved ASP sidechain, serine65, and conserved H68 and N71 of cyt b.
Also, there is a strong H-bond from OG of S65 to carboxylate of D67, locking 1 turn of helix? carbonyls of 65, 66 in 3-10 or alpha helical pattern

3 residues involved here- beef cyt b:H68 and ISP:D67 and S65,  (Yeast cyb: H67, isp: D87, S85). Cyt b D/N 71/72/73 is involved with only its carbonyl oxygen, the side chain binds cyt c1. This arrangement is present in stig or azx structures, so 67 is nearly imobile.

TM Helix ends ~ #61. (R59 and before carbonyls are in helix H-bonding.  The random coil between 61 and 65 is stabilized by H-bonds from cyt b C:W163NE2,  P:H54, C:R177, and P:N74  and  to the backbone carbonyls of ISP:59, 61, 62, and 64+60. (cyt b C:W164, P:H55,C:R178,P:Q75 in chicken)(C:W164, P:H53,C:R178,P:H73 in yeast)
R63 H-bonds a waters. (323 and 11 on R side, 160 and 8 on E side)
(His rotamer 1 for P54, rot 4 for P68)

Tether helix - - -

Arg92 and Trp91 H-bond to backbone (extending the beta strand?) down to 72, maybe 71 bovine.
71 may pepflip during movement. In one orientation could bind R92.
Not extending the beta strand- 74-78 is in sheet with 184-196, not 92!
Mutants with a double cysteine
substitution at Ala42 and Val44 (ADV-CDC) or at
Pro40 and Ala42 (PSA-CSC) have a retarded (50%) or no
photosynthetic growth rate

Mutants with a double cysteine
substitution at Ala42 and Val44 (ADV-CDC) or at
Pro40 and Ala42 (PSA-CSC) have a retarded (50%) or no
photosynthetic growth rate
(thats 64, 66, 68 bovine)

69 is the first residue with significant movement, comparing stig and azx structures.
maybe 68- the H-bond from 65-68 stretches from <3A to 3.7 on adding stig.
(with famox 65 still H-bonds 68 and 69; 66 still H-bonds 70)

In the azx structure there is alpha-helix structure involving carbonyls of 65,66
	(65 also Hbonds 68)
3-10 helix involving carbonyls of 68, 69
carbonyl of 67 doesnt make any helical H-bond.

===
neck mutations:
PRO or GLY replacements lead to Qo-locked species.

sensitivity to proteolysis not affected by stg, myx. Normally stig inhibits- because protease specific for helix? pro and gly might eliminate helix, but +3ala should promote it.

deletion revertant from the 6pro mutant shows lower mobility of the ed (c1 rereduction in presence myxo) - because not as extensible? no extension needed to visit Qo site, retraction for c1.

extension, helical propensity instead of flexibility
binding disruption vs barrier/obstruction to movement for ef loop.