Table 1. List of separate structures found in the 3-D map.

Structure	Symbol	Repeat	Location
Protofilament	PF(1–13)	4 nm	Forms a 13-protofilament microtubule
Axis-facing sheet	A	3 domains in 16 nm	Microribbon, attaches to P7 at base
Inner sheet	I	16 nm	Microribbon, attaches to P8 at base
Margin-facing sheet	M	16 nm	Microribbon, attaches to P9 at base
Crossbridge	CB	16 nm	Connects A to M of adjacent microribbons
Side rail	SR	Fibrous (continuous)	Completely along outer surface of PF6
Bridge	B	16 nm	Connects SR to A
Side-arm	SA	8 nm	Spans PF9-PF12
Paddle	P	8 nm	PF13 (with PF1, location of seam)
Giardial microtubule-associated protein 1	gMAP1	8 nm	PF1 (with PF13, location of seam)
Giardial microtubule-associated protein 2	gMAP2	8 nm	PF2
Giardial microtubule-associated protein 3	gMAP3	8 nm	PF3
Giardial microtubule inner protein 5	gMIP5	8 nm	PF5
Giardial microtubule inner protein 7	gMIP7	8 nm	PF7
Giardial microtubule inner protein 8	gMIP8	3 domains in 8 nm	PF8

The averaging procedure was based on a 16 nm long repetitive volume along the microtubule axis that comprised two consecutive tubulin dimers. A single tubulin monomer is 4 nm, a single αβ-tubulin dimer is 8 nm, and two αβ-tubulin dimers are 16 nm.